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 $247.30   5.460%   $260.8026   $260.80   $260.80   $260.80  
  Purchase #2 $63.34   8.851%   $68.9462   $68.95   $68.95   $68.90  
  Purchase #3 $225.92   7.243%   $242.2834   $242.28   $242.30   $242.30  
  Purchase #4 $201.55   5.355%   $212.343   $212.34   $212.35   $212.30  
  Purchase #5 $125.29   3.391%   $129.5386   $129.54   $129.55   $129.50  
  Purchase #6 $168.89   5.504%   $178.1857   $178.19   $178.20   $178.20  
  Purchase #7 $132.44   6.631%   $141.2221   $141.22   $141.20   $141.20  
  7 purchase totals = $1,164.73       $1,233.3216   $1,233.32   $1,233.35   $1,233.20