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 $62.94   3.800%   $65.3317   $65.33   $65.35   $65.30  
  Purchase #2 $65.62   8.327%   $71.0842   $71.08   $71.10   $71.10  
  Purchase #3 $237.35   12.296%   $266.5346   $266.53   $266.55   $266.50  
  Purchase #4 $45.73   4.650%   $47.8564   $47.86   $47.85   $47.90  
  Purchase #5 $218.88   9.368%   $239.3847   $239.38   $239.40   $239.40  
  Purchase #6 $161.28   8.872%   $175.5888   $175.59   $175.60   $175.60  
  Purchase #7 $92.26   3.696%   $95.6699   $95.67   $95.65   $95.70  
  7 purchase totals = $884.06       $961.4503   $961.44   $961.50   $961.50