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 $200.94   6.756%   $214.5155   $214.52   $214.50   $214.50  
  Purchase #2 $108.57   11.592%   $121.1554   $121.16   $121.15   $121.20  
  Purchase #3 $50.53   6.524%   $53.8266   $53.83   $53.85   $53.80  
  Purchase #4 $99.33   13.352%   $112.5925   $112.59   $112.60   $112.60  
  Purchase #5 $54.35   7.139%   $58.23   $58.23   $58.25   $58.20  
  Purchase #6 $249.83   3.124%   $257.6347   $257.63   $257.65   $257.60  
  Purchase #7 $193.37   5.429%   $203.8681   $203.87   $203.85   $203.90  
  7 purchase totals = $956.92       $1,021.8228   $1,021.83   $1,021.85   $1,021.80