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 $56.26   11.727%   $62.8576   $62.86   $62.85   $62.90  
  Purchase #2 $123.64   13.746%   $140.6356   $140.64   $140.65   $140.60  
  Purchase #3 $206.53   4.852%   $216.5508   $216.55   $216.55   $216.60  
  Purchase #4 $34.66   11.599%   $38.6802   $38.68   $38.70   $38.70  
  Purchase #5 $187.25   4.584%   $195.8335   $195.83   $195.85   $195.80  
  Purchase #6 $131.27   4.809%   $137.5828   $137.58   $137.60   $137.60  
  Purchase #7 $190.38   8.188%   $205.9683   $205.97   $205.95   $206.00  
  7 purchase totals = $929.99       $998.1088   $998.11   $998.15   $998.20