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 $76.58   13.180%   $86.6732   $86.67   $86.65   $86.70  
  Purchase #2 $183.50   5.468%   $193.5338   $193.53   $193.55   $193.50  
  Purchase #3 $195.33   5.223%   $205.5321   $205.53   $205.55   $205.50  
  Purchase #4 $41.38   4.794%   $43.3638   $43.36   $43.35   $43.40  
  Purchase #5 $53.84   3.415%   $55.6786   $55.68   $55.70   $55.70  
  Purchase #6 $110.71   11.139%   $123.042   $123.04   $123.05   $123.00  
  Purchase #7 $89.46   5.451%   $94.3365   $94.34   $94.35   $94.30  
  7 purchase totals = $750.80       $802.1600   $802.15   $802.20   $802.10