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 $56.84   8.686%   $61.7771   $61.78   $61.80   $61.80  
  Purchase #2 $210.47   3.540%   $217.9206   $217.92   $217.90   $217.90  
  Purchase #3 $241.76   5.644%   $255.4049   $255.40   $255.40   $255.40  
  Purchase #4 $231.51   9.453%   $253.3946   $253.39   $253.40   $253.40  
  Purchase #5 $191.58   11.563%   $213.7324   $213.73   $213.75   $213.70  
  Purchase #6 $65.80   6.308%   $69.9507   $69.95   $69.95   $70.00  
  Purchase #7 $50.97   3.605%   $52.8075   $52.81   $52.80   $52.80  
  7 purchase totals = $1,048.93       $1,124.9878   $1,124.98   $1,125.00   $1,125.00