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 $59.97   8.396%   $65.0051   $65.01   $65.00   $65.00  
  Purchase #2 $62.88   12.130%   $70.5073   $70.51   $70.50   $70.50  
  Purchase #3 $77.39   13.229%   $87.6279   $87.63   $87.65   $87.60  
  Purchase #4 $192.70   9.535%   $211.0739   $211.07   $211.05   $211.10  
  Purchase #5 $169.30   7.834%   $182.563   $182.56   $182.55   $182.60  
  Purchase #6 $24.76   4.658%   $25.9133   $25.91   $25.90   $25.90  
  Purchase #7 $73.28   12.712%   $82.5954   $82.60   $82.60   $82.60  
  7 purchase totals = $660.28       $725.2859   $725.29   $725.25   $725.30