Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $116.53   8.380%   $126.2952   $126.30   $126.30   $126.30  
  Purchase #2 $241.27   12.844%   $272.2587   $272.26   $272.25   $272.30  
  Purchase #3 $126.58   5.268%   $133.2482   $133.25   $133.25   $133.20  
  Purchase #4 $198.28   11.249%   $220.5845   $220.58   $220.60   $220.60  
  Purchase #5 $196.31   9.655%   $215.2637   $215.26   $215.25   $215.30  
  Purchase #6 $202.67   12.736%   $228.4821   $228.48   $228.50   $228.50  
  Purchase #7 $218.69   11.426%   $243.6775   $243.68   $243.70   $243.70  
  7 purchase totals = $1,300.33       $1,439.8099   $1,439.81   $1,439.85   $1,439.90