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 $217.83   12.334%   $244.6972   $244.70   $244.70   $244.70  
  Purchase #2 $149.49   8.545%   $162.2639   $162.26   $162.25   $162.30  
  Purchase #3 $32.88   6.459%   $35.0037   $35.00   $35.00   $35.00  
  Purchase #4 $244.73   8.206%   $264.8125   $264.81   $264.80   $264.80  
  Purchase #5 $43.49   5.748%   $45.9898   $45.99   $46.00   $46.00  
  Purchase #6 $41.37   13.632%   $47.0096   $47.01   $47.00   $47.00  
  Purchase #7 $196.45   3.274%   $202.8818   $202.88   $202.90   $202.90  
  7 purchase totals = $926.24       $1,002.6585   $1,002.65   $1,002.65   $1,002.70