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 $248.75   11.144%   $276.4707   $276.47   $276.45   $276.50  
  Purchase #2 $125.38   3.568%   $129.8536   $129.85   $129.85   $129.90  
  Purchase #3 $141.80   11.186%   $157.6617   $157.66   $157.65   $157.70  
  Purchase #4 $94.58   3.489%   $97.8799   $97.88   $97.90   $97.90  
  Purchase #5 $22.80   9.325%   $24.9261   $24.93   $24.95   $24.90  
  Purchase #6 $47.28   4.752%   $49.5267   $49.53   $49.55   $49.50  
  Purchase #7 $189.33   6.689%   $201.9943   $201.99   $202.00   $202.00  
  7 purchase totals = $869.92       $938.3130   $938.31   $938.35   $938.40