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 $92.92   4.555%   $97.1525   $97.15   $97.15   $97.20  
  Purchase #2 $98.71   12.195%   $110.7477   $110.75   $110.75   $110.70  
  Purchase #3 $180.50   13.552%   $204.9614   $204.96   $204.95   $205.00  
  Purchase #4 $208.74   4.557%   $218.2523   $218.25   $218.25   $218.30  
  Purchase #5 $187.97   8.367%   $203.6974   $203.70   $203.70   $203.70  
  Purchase #6 $45.87   9.794%   $50.3625   $50.36   $50.35   $50.40  
  Purchase #7 $61.57   8.669%   $66.9075   $66.91   $66.90   $66.90  
  7 purchase totals = $876.28       $952.0813   $952.08   $952.05   $952.20