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 $163.64   13.252%   $185.3256   $185.33   $185.35   $185.30  
  Purchase #2 $33.44   3.499%   $34.6101   $34.61   $34.60   $34.60  
  Purchase #3 $111.51   7.609%   $119.9948   $119.99   $120.00   $120.00  
  Purchase #4 $112.31   11.259%   $124.955   $124.96   $124.95   $125.00  
  Purchase #5 $239.97   7.264%   $257.4014   $257.40   $257.40   $257.40  
  Purchase #6 $126.45   9.619%   $138.6132   $138.61   $138.60   $138.60  
  Purchase #7 $204.27   4.733%   $213.9381   $213.94   $213.95   $213.90  
  7 purchase totals = $991.59       $1,074.8382   $1,074.84   $1,074.85   $1,074.80