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 $46.90   6.427%   $49.9143   $49.91   $49.90   $49.90  
  Purchase #2 $177.84   13.576%   $201.9836   $201.98   $202.00   $202.00  
  Purchase #3 $159.27   10.749%   $176.3899   $176.39   $176.40   $176.40  
  Purchase #4 $117.71   13.573%   $133.6868   $133.69   $133.70   $133.70  
  Purchase #5 $180.40   3.758%   $187.1794   $187.18   $187.20   $187.20  
  Purchase #6 $26.66   7.205%   $28.5809   $28.58   $28.60   $28.60  
  Purchase #7 $111.37   6.111%   $118.1758   $118.18   $118.20   $118.20  
  7 purchase totals = $820.15       $895.9107   $895.91   $896.00   $896.00