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 $236.98   11.673%   $264.6427   $264.64   $264.65   $264.60  
  Purchase #2 $85.92   8.502%   $93.2249   $93.22   $93.20   $93.20  
  Purchase #3 $239.28   7.674%   $257.6423   $257.64   $257.65   $257.60  
  Purchase #4 $51.94   6.271%   $55.1972   $55.20   $55.20   $55.20  
  Purchase #5 $221.68   8.299%   $240.0772   $240.08   $240.10   $240.10  
  Purchase #6 $85.67   3.347%   $88.5374   $88.54   $88.55   $88.50  
  Purchase #7 $59.38   12.377%   $66.7295   $66.73   $66.75   $66.70  
  7 purchase totals = $980.85       $1,066.0512   $1,066.05   $1,066.10   $1,065.90