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 $53.83   9.853%   $59.1339   $59.13   $59.15   $59.10  
  Purchase #2 $165.96   10.855%   $183.975   $183.98   $184.00   $184.00  
  Purchase #3 $156.87   7.617%   $168.8188   $168.82   $168.80   $168.80  
  Purchase #4 $127.40   7.491%   $136.9435   $136.94   $136.95   $136.90  
  Purchase #5 $194.54   3.825%   $201.9812   $201.98   $202.00   $202.00  
  Purchase #6 $47.29   4.249%   $49.2994   $49.30   $49.30   $49.30  
  Purchase #7 $194.36   8.218%   $210.3325   $210.33   $210.35   $210.30  
  7 purchase totals = $940.25       $1,010.4843   $1,010.48   $1,010.55   $1,010.40