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 $229.56   10.321%   $253.2529   $253.25   $253.25   $253.30  
  Purchase #2 $102.32   3.779%   $106.1867   $106.19   $106.20   $106.20  
  Purchase #3 $159.89   11.114%   $177.6602   $177.66   $177.65   $177.70  
  Purchase #4 $79.31   12.775%   $89.4419   $89.44   $89.45   $89.40  
  Purchase #5 $43.71   7.226%   $46.8685   $46.87   $46.85   $46.90  
  Purchase #6 $147.44   11.565%   $164.4914   $164.49   $164.50   $164.50  
  Purchase #7 $205.55   4.221%   $214.2263   $214.23   $214.25   $214.20  
  7 purchase totals = $967.78       $1,052.1279   $1,052.13   $1,052.15   $1,052.20