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 $48.57   12.174%   $54.4829   $54.48   $54.50   $54.50  
  Purchase #2 $192.41   3.771%   $199.6658   $199.67   $199.65   $199.70  
  Purchase #3 $94.50   8.127%   $102.18   $102.18   $102.20   $102.20  
  Purchase #4 $99.66   13.217%   $112.8321   $112.83   $112.85   $112.80  
  Purchase #5 $102.59   10.817%   $113.6872   $113.69   $113.70   $113.70  
  Purchase #6 $180.61   11.828%   $201.9726   $201.97   $201.95   $202.00  
  Purchase #7 $137.26   12.610%   $154.5685   $154.57   $154.55   $154.60  
  7 purchase totals = $855.60       $939.3891   $939.39   $939.40   $939.50