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 $142.29   12.177%   $159.6167   $159.62   $159.60   $159.60  
  Purchase #2 $211.54   11.158%   $235.1436   $235.14   $235.15   $235.10  
  Purchase #3 $136.51   10.487%   $150.8258   $150.83   $150.85   $150.80  
  Purchase #4 $126.66   11.720%   $141.5046   $141.50   $141.50   $141.50  
  Purchase #5 $202.56   13.390%   $229.6828   $229.68   $229.70   $229.70  
  Purchase #6 $161.78   12.630%   $182.2128   $182.21   $182.20   $182.20  
  Purchase #7 $66.85   13.324%   $75.7571   $75.76   $75.75   $75.80  
  7 purchase totals = $1,048.19       $1,174.7434   $1,174.74   $1,174.75   $1,174.70