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 $153.71   10.811%   $170.3276   $170.33   $170.35   $170.30  
  Purchase #2 $51.81   3.357%   $53.5493   $53.55   $53.55   $53.50  
  Purchase #3 $80.92   9.576%   $88.6689   $88.67   $88.65   $88.70  
  Purchase #4 $231.98   13.358%   $262.9679   $262.97   $262.95   $263.00  
  Purchase #5 $12.34   13.843%   $14.0482   $14.05   $14.05   $14.00  
  Purchase #6 $117.43   7.229%   $125.919   $125.92   $125.90   $125.90  
  Purchase #7 $152.79   4.409%   $159.5265   $159.53   $159.55   $159.50  
  7 purchase totals = $800.98       $875.0074   $875.02   $875.00   $874.90