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 $246.66   5.787%   $260.9342   $260.93   $260.95   $260.90  
  Purchase #2 $129.63   11.351%   $144.3443   $144.34   $144.35   $144.30  
  Purchase #3 $201.75   3.664%   $209.1421   $209.14   $209.15   $209.10  
  Purchase #4 $44.55   7.460%   $47.8734   $47.87   $47.85   $47.90  
  Purchase #5 $67.26   7.388%   $72.2292   $72.23   $72.25   $72.20  
  Purchase #6 $248.45   7.646%   $267.4465   $267.45   $267.45   $267.40  
  Purchase #7 $60.35   7.557%   $64.9106   $64.91   $64.90   $64.90  
  7 purchase totals = $998.65       $1,066.8803   $1,066.87   $1,066.90   $1,066.70