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 $66.35   13.408%   $75.2462   $75.25   $75.25   $75.20  
  Purchase #2 $120.27   5.335%   $126.6864   $126.69   $126.70   $126.70  
  Purchase #3 $101.26   11.407%   $112.8107   $112.81   $112.80   $112.80  
  Purchase #4 $186.26   13.742%   $211.8558   $211.86   $211.85   $211.90  
  Purchase #5 $200.37   9.568%   $219.5414   $219.54   $219.55   $219.50  
  Purchase #6 $152.45   5.418%   $160.7097   $160.71   $160.70   $160.70  
  Purchase #7 $54.56   7.211%   $58.4943   $58.49   $58.50   $58.50  
  7 purchase totals = $881.52       $965.3445   $965.35   $965.35   $965.30