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 $54.96   6.861%   $58.7308   $58.73   $58.75   $58.70  
  Purchase #2 $242.36   9.415%   $265.1782   $265.18   $265.20   $265.20  
  Purchase #3 $234.38   11.597%   $261.561   $261.56   $261.55   $261.60  
  Purchase #4 $112.58   3.110%   $116.0812   $116.08   $116.10   $116.10  
  Purchase #5 $129.29   11.328%   $143.936   $143.94   $143.95   $143.90  
  Purchase #6 $132.39   12.430%   $148.8461   $148.85   $148.85   $148.80  
  Purchase #7 $37.29   4.559%   $38.9901   $38.99   $39.00   $39.00  
  7 purchase totals = $943.25       $1,033.3234   $1,033.33   $1,033.40   $1,033.30