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 $207.31   8.507%   $224.9459   $224.95   $224.95   $224.90  
  Purchase #2 $180.69   12.327%   $202.9637   $202.96   $202.95   $203.00  
  Purchase #3 $244.32   13.864%   $278.1925   $278.19   $278.20   $278.20  
  Purchase #4 $74.84   10.124%   $82.4168   $82.42   $82.40   $82.40  
  Purchase #5 $70.77   3.375%   $73.1585   $73.16   $73.15   $73.20  
  Purchase #6 $225.51   7.151%   $241.6362   $241.64   $241.65   $241.60  
  Purchase #7 $94.37   4.732%   $98.8356   $98.84   $98.85   $98.80  
  7 purchase totals = $1,097.81       $1,202.1492   $1,202.16   $1,202.15   $1,202.10