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 $58.43   8.589%   $63.4486   $63.45   $63.45   $63.40  
  Purchase #2 $102.26   11.700%   $114.2244   $114.22   $114.20   $114.20  
  Purchase #3 $51.75   13.550%   $58.7621   $58.76   $58.75   $58.80  
  Purchase #4 $239.56   13.123%   $270.9975   $271.00   $271.00   $271.00  
  Purchase #5 $25.50   4.650%   $26.6858   $26.69   $26.70   $26.70  
  Purchase #6 $203.56   10.816%   $225.577   $225.58   $225.60   $225.60  
  Purchase #7 $109.97   5.739%   $116.2812   $116.28   $116.30   $116.30  
  7 purchase totals = $791.03       $875.9766   $875.98   $876.00   $876.00