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 $24.84   3.372%   $25.6776   $25.68   $25.70   $25.70  
  Purchase #2 $211.98   6.164%   $225.0464   $225.05   $225.05   $225.00  
  Purchase #3 $46.49   6.223%   $49.3831   $49.38   $49.40   $49.40  
  Purchase #4 $157.92   8.504%   $171.3495   $171.35   $171.35   $171.30  
  Purchase #5 $138.32   5.800%   $146.3426   $146.34   $146.35   $146.30  
  Purchase #6 $237.56   3.540%   $245.9696   $245.97   $245.95   $246.00  
  Purchase #7 $51.91   10.404%   $57.3107   $57.31   $57.30   $57.30  
  7 purchase totals = $869.02       $921.0795   $921.08   $921.10   $921.00