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 $169.85   10.422%   $187.5518   $187.55   $187.55   $187.60  
  Purchase #2 $120.94   11.397%   $134.7235   $134.72   $134.70   $134.70  
  Purchase #3 $105.44   11.430%   $117.4918   $117.49   $117.50   $117.50  
  Purchase #4 $161.46   11.502%   $180.0311   $180.03   $180.05   $180.00  
  Purchase #5 $194.96   9.622%   $213.7191   $213.72   $213.70   $213.70  
  Purchase #6 $28.26   8.334%   $30.6152   $30.62   $30.60   $30.60  
  Purchase #7 $87.44   11.118%   $97.1616   $97.16   $97.15   $97.20  
  7 purchase totals = $868.35       $961.2941   $961.29   $961.25   $961.30