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 $186.42   9.862%   $204.8047   $204.80   $204.80   $204.80  
  Purchase #2 $87.63   12.282%   $98.3927   $98.39   $98.40   $98.40  
  Purchase #3 $182.57   7.715%   $196.6553   $196.66   $196.65   $196.70  
  Purchase #4 $218.81   11.364%   $243.6756   $243.68   $243.70   $243.70  
  Purchase #5 $28.40   6.807%   $30.3332   $30.33   $30.35   $30.30  
  Purchase #6 $65.85   6.469%   $70.1098   $70.11   $70.10   $70.10  
  Purchase #7 $160.26   6.356%   $170.4461   $170.45   $170.45   $170.40  
  7 purchase totals = $929.94       $1,014.4174   $1,014.42   $1,014.45   $1,014.40