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 $166.94   4.833%   $175.0082   $175.01   $175.00   $175.00  
  Purchase #2 $54.90   10.373%   $60.5948   $60.59   $60.60   $60.60  
  Purchase #3 $113.43   10.792%   $125.6714   $125.67   $125.65   $125.70  
  Purchase #4 $168.97   12.618%   $190.2906   $190.29   $190.30   $190.30  
  Purchase #5 $9.40   9.619%   $10.3042   $10.30   $10.30   $10.30  
  Purchase #6 $68.45   3.771%   $71.0312   $71.03   $71.05   $71.00  
  Purchase #7 $187.51   5.723%   $198.2412   $198.24   $198.25   $198.20  
  7 purchase totals = $769.60       $831.1416   $831.13   $831.15   $831.10