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 $60.74   13.588%   $68.9934   $68.99   $69.00   $69.00  
  Purchase #2 $160.94   13.413%   $182.5269   $182.53   $182.55   $182.50  
  Purchase #3 $85.53   10.516%   $94.5243   $94.52   $94.50   $94.50  
  Purchase #4 $100.29   7.196%   $107.5069   $107.51   $107.50   $107.50  
  Purchase #5 $153.82   12.809%   $173.5228   $173.52   $173.50   $173.50  
  Purchase #6 $111.56   7.235%   $119.6314   $119.63   $119.65   $119.60  
  Purchase #7 $158.49   9.633%   $173.7573   $173.76   $173.75   $173.80  
  7 purchase totals = $831.37       $920.4630   $920.46   $920.45   $920.40