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 $173.39   6.723%   $185.047   $185.05   $185.05   $185.00  
  Purchase #2 $88.60   10.152%   $97.5947   $97.59   $97.60   $97.60  
  Purchase #3 $155.43   3.340%   $160.6214   $160.62   $160.60   $160.60  
  Purchase #4 $60.62   4.730%   $63.4873   $63.49   $63.50   $63.50  
  Purchase #5 $189.58   11.248%   $210.904   $210.90   $210.90   $210.90  
  Purchase #6 $163.86   9.860%   $180.0166   $180.02   $180.00   $180.00  
  Purchase #7 $62.80   3.407%   $64.9396   $64.94   $64.95   $64.90  
  7 purchase totals = $894.28       $962.6106   $962.61   $962.60   $962.50