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 $58.84   3.644%   $60.9841   $60.98   $61.00   $61.00  
  Purchase #2 $51.42   13.594%   $58.41   $58.41   $58.40   $58.40  
  Purchase #3 $166.88   5.519%   $176.0901   $176.09   $176.10   $176.10  
  Purchase #4 $211.74   7.554%   $227.7348   $227.73   $227.75   $227.70  
  Purchase #5 $44.58   5.711%   $47.126   $47.13   $47.15   $47.10  
  Purchase #6 $182.61   11.192%   $203.0477   $203.05   $203.05   $203.00  
  Purchase #7 $60.80   3.170%   $62.7274   $62.73   $62.75   $62.70  
  7 purchase totals = $776.87       $836.1201   $836.12   $836.20   $836.00