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 $119.70   11.727%   $133.7372   $133.74   $133.75   $133.70  
  Purchase #2 $203.60   10.743%   $225.4727   $225.47   $225.45   $225.50  
  Purchase #3 $151.72   8.240%   $164.2217   $164.22   $164.20   $164.20  
  Purchase #4 $198.98   3.250%   $205.4469   $205.45   $205.45   $205.40  
  Purchase #5 $192.36   6.463%   $204.7922   $204.79   $204.80   $204.80  
  Purchase #6 $60.29   7.148%   $64.5995   $64.60   $64.60   $64.60  
  Purchase #7 $220.76   12.719%   $248.8385   $248.84   $248.85   $248.80  
  7 purchase totals = $1,147.41       $1,247.1087   $1,247.11   $1,247.10   $1,247.00