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 $54.75   6.760%   $58.4511   $58.45   $58.45   $58.50  
  Purchase #2 $245.62   9.426%   $268.7721   $268.77   $268.75   $268.80  
  Purchase #3 $218.76   9.784%   $240.1635   $240.16   $240.15   $240.20  
  Purchase #4 $226.87   8.810%   $246.8572   $246.86   $246.85   $246.90  
  Purchase #5 $69.56   4.384%   $72.6095   $72.61   $72.60   $72.60  
  Purchase #6 $61.26   5.155%   $64.418   $64.42   $64.40   $64.40  
  Purchase #7 $24.47   4.614%   $25.599   $25.60   $25.60   $25.60  
  7 purchase totals = $901.29       $976.8704   $976.87   $976.80   $977.00