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 $202.58   7.302%   $217.3724   $217.37   $217.35   $217.40  
  Purchase #2 $180.38   11.552%   $201.2175   $201.22   $201.20   $201.20  
  Purchase #3 $32.88   10.123%   $36.2084   $36.21   $36.20   $36.20  
  Purchase #4 $187.89   13.680%   $213.5934   $213.59   $213.60   $213.60  
  Purchase #5 $8.56   5.439%   $9.0256   $9.03   $9.05   $9.00  
  Purchase #6 $211.78   13.483%   $240.3343   $240.33   $240.35   $240.30  
  Purchase #7 $103.40   12.311%   $116.1296   $116.13   $116.15   $116.10  
  7 purchase totals = $927.47       $1,033.8812   $1,033.88   $1,033.90   $1,033.80