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 $191.87   6.336%   $204.0269   $204.03   $204.05   $204.00  
  Purchase #2 $200.93   10.307%   $221.6399   $221.64   $221.65   $221.60  
  Purchase #3 $43.98   13.529%   $49.9301   $49.93   $49.95   $49.90  
  Purchase #4 $247.34   7.365%   $265.5566   $265.56   $265.55   $265.60  
  Purchase #5 $13.93   9.414%   $15.2414   $15.24   $15.25   $15.20  
  Purchase #6 $21.78   6.130%   $23.1151   $23.12   $23.10   $23.10  
  Purchase #7 $45.32   9.338%   $49.552   $49.55   $49.55   $49.60  
  7 purchase totals = $765.15       $829.0620   $829.07   $829.10   $829.00