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 $246.88   7.475%   $265.3343   $265.33   $265.35   $265.30  
  Purchase #2 $91.65   11.667%   $102.3428   $102.34   $102.35   $102.30  
  Purchase #3 $183.99   10.256%   $202.86   $202.86   $202.85   $202.90  
  Purchase #4 $9.28   4.678%   $9.7141   $9.71   $9.70   $9.70  
  Purchase #5 $123.46   6.344%   $131.2923   $131.29   $131.30   $131.30  
  Purchase #6 $41.95   4.525%   $43.8482   $43.85   $43.85   $43.80  
  Purchase #7 $66.26   8.485%   $71.8822   $71.88   $71.90   $71.90  
  7 purchase totals = $763.47       $827.2739   $827.26   $827.30   $827.20