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 $241.94   13.336%   $274.2051   $274.21   $274.20   $274.20  
  Purchase #2 $118.69   9.412%   $129.8611   $129.86   $129.85   $129.90  
  Purchase #3 $163.53   11.755%   $182.753   $182.75   $182.75   $182.80  
  Purchase #4 $27.63   13.345%   $31.3172   $31.32   $31.30   $31.30  
  Purchase #5 $197.66   11.231%   $219.8592   $219.86   $219.85   $219.90  
  Purchase #6 $161.32   8.519%   $175.0629   $175.06   $175.05   $175.10  
  Purchase #7 $124.75   4.379%   $130.2128   $130.21   $130.20   $130.20  
  7 purchase totals = $1,035.52       $1,143.2713   $1,143.27   $1,143.20   $1,143.40