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 $233.83   3.477%   $241.9603   $241.96   $241.95   $242.00  
  Purchase #2 $197.55   3.442%   $204.3497   $204.35   $204.35   $204.30  
  Purchase #3 $241.64   13.720%   $274.793   $274.79   $274.80   $274.80  
  Purchase #4 $19.32   4.832%   $20.2535   $20.25   $20.25   $20.30  
  Purchase #5 $207.68   8.267%   $224.8489   $224.85   $224.85   $224.80  
  Purchase #6 $92.33   13.234%   $104.549   $104.55   $104.55   $104.50  
  Purchase #7 $170.29   3.285%   $175.884   $175.88   $175.90   $175.90  
  7 purchase totals = $1,162.64       $1,246.6384   $1,246.63   $1,246.65   $1,246.60