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 $194.36   5.630%   $205.3025   $205.30   $205.30   $205.30  
  Purchase #2 $132.92   3.793%   $137.9617   $137.96   $137.95   $138.00  
  Purchase #3 $231.57   6.122%   $245.7467   $245.75   $245.75   $245.70  
  Purchase #4 $124.98   8.211%   $135.2421   $135.24   $135.25   $135.20  
  Purchase #5 $46.75   13.711%   $53.1599   $53.16   $53.15   $53.20  
  Purchase #6 $221.30   11.308%   $246.3246   $246.32   $246.30   $246.30  
  Purchase #7 $218.93   6.408%   $232.959   $232.96   $232.95   $233.00  
  7 purchase totals = $1,170.81       $1,256.6965   $1,256.69   $1,256.65   $1,256.70