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 $222.64   8.336%   $241.1993   $241.20   $241.20   $241.20  
  Purchase #2 $88.61   9.281%   $96.8339   $96.83   $96.85   $96.80  
  Purchase #3 $222.29   9.267%   $242.8896   $242.89   $242.90   $242.90  
  Purchase #4 $27.68   3.155%   $28.5533   $28.55   $28.55   $28.60  
  Purchase #5 $203.28   3.624%   $210.6469   $210.65   $210.65   $210.60  
  Purchase #6 $79.65   3.246%   $82.2354   $82.24   $82.25   $82.20  
  Purchase #7 $132.35   6.466%   $140.9078   $140.91   $140.90   $140.90  
  7 purchase totals = $976.50       $1,043.2662   $1,043.27   $1,043.30   $1,043.20