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 $218.51   6.703%   $233.1567   $233.16   $233.15   $233.20  
  Purchase #2 $248.84   10.415%   $274.7567   $274.76   $274.75   $274.80  
  Purchase #3 $49.45   4.513%   $51.6817   $51.68   $51.70   $51.70  
  Purchase #4 $143.48   8.827%   $156.145   $156.15   $156.15   $156.10  
  Purchase #5 $26.98   4.233%   $28.1221   $28.12   $28.10   $28.10  
  Purchase #6 $38.80   6.219%   $41.213   $41.21   $41.20   $41.20  
  Purchase #7 $46.43   7.340%   $49.838   $49.84   $49.85   $49.80  
  7 purchase totals = $772.49       $834.9132   $834.92   $834.90   $834.90