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 $191.66   4.462%   $200.2119   $200.21   $200.20   $200.20  
  Purchase #2 $228.95   12.188%   $256.8544   $256.85   $256.85   $256.90  
  Purchase #3 $244.69   10.473%   $270.3164   $270.32   $270.30   $270.30  
  Purchase #4 $58.29   8.758%   $63.395   $63.40   $63.40   $63.40  
  Purchase #5 $162.65   9.351%   $177.8594   $177.86   $177.85   $177.90  
  Purchase #6 $123.89   6.859%   $132.3876   $132.39   $132.40   $132.40  
  Purchase #7 $226.90   7.311%   $243.4887   $243.49   $243.50   $243.50  
  7 purchase totals = $1,237.03       $1,344.5134   $1,344.52   $1,344.50   $1,344.60