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 $193.65   8.602%   $210.3078   $210.31   $210.30   $210.30  
  Purchase #2 $112.38   8.822%   $122.2942   $122.29   $122.30   $122.30  
  Purchase #3 $193.79   8.146%   $209.5761   $209.58   $209.60   $209.60  
  Purchase #4 $109.85   7.422%   $118.0031   $118.00   $118.00   $118.00  
  Purchase #5 $118.68   4.121%   $123.5708   $123.57   $123.55   $123.60  
  Purchase #6 $62.44   8.844%   $67.9622   $67.96   $67.95   $68.00  
  Purchase #7 $146.55   9.631%   $160.6642   $160.66   $160.65   $160.70  
  7 purchase totals = $937.34       $1,012.3784   $1,012.37   $1,012.35   $1,012.50