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 $22.56   5.327%   $23.7618   $23.76   $23.75   $23.80  
  Purchase #2 $191.89   11.388%   $213.7424   $213.74   $213.75   $213.70  
  Purchase #3 $55.95   5.448%   $58.9982   $59.00   $59.00   $59.00  
  Purchase #4 $67.40   10.545%   $74.5073   $74.51   $74.50   $74.50  
  Purchase #5 $207.67   12.399%   $233.419   $233.42   $233.40   $233.40  
  Purchase #6 $125.52   5.856%   $132.8705   $132.87   $132.85   $132.90  
  Purchase #7 $136.65   5.372%   $143.9908   $143.99   $144.00   $144.00  
  7 purchase totals = $807.64       $881.2900   $881.29   $881.25   $881.30