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 $228.60   3.816%   $237.3234   $237.32   $237.30   $237.30  
  Purchase #2 $165.31   3.403%   $170.9355   $170.94   $170.95   $170.90  
  Purchase #3 $54.44   4.238%   $56.7472   $56.75   $56.75   $56.70  
  Purchase #4 $61.73   12.484%   $69.4364   $69.44   $69.45   $69.40  
  Purchase #5 $34.39   5.552%   $36.2993   $36.30   $36.30   $36.30  
  Purchase #6 $195.83   6.191%   $207.9538   $207.95   $207.95   $208.00  
  Purchase #7 $87.93   12.387%   $98.8219   $98.82   $98.80   $98.80  
  7 purchase totals = $828.23       $877.5175   $877.52   $877.50   $877.40