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 $135.80   8.439%   $147.2602   $147.26   $147.25   $147.30  
  Purchase #2 $237.69   9.446%   $260.1422   $260.14   $260.15   $260.10  
  Purchase #3 $54.54   13.601%   $61.958   $61.96   $61.95   $62.00  
  Purchase #4 $136.73   9.118%   $149.197   $149.20   $149.20   $149.20  
  Purchase #5 $203.48   6.222%   $216.1405   $216.14   $216.15   $216.10  
  Purchase #6 $125.48   3.824%   $130.2784   $130.28   $130.30   $130.30  
  Purchase #7 $141.91   4.432%   $148.1995   $148.20   $148.20   $148.20  
  7 purchase totals = $1,035.63       $1,113.1758   $1,113.18   $1,113.20   $1,113.20