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 $153.76   8.367%   $166.6251   $166.63   $166.65   $166.60  
  Purchase #2 $185.78   8.592%   $201.7422   $201.74   $201.75   $201.70  
  Purchase #3 $94.61   4.393%   $98.7662   $98.77   $98.75   $98.80  
  Purchase #4 $157.77   6.431%   $167.9162   $167.92   $167.90   $167.90  
  Purchase #5 $221.55   8.733%   $240.898   $240.90   $240.90   $240.90  
  Purchase #6 $104.56   5.468%   $110.2773   $110.28   $110.30   $110.30  
  Purchase #7 $207.53   13.616%   $235.7873   $235.79   $235.80   $235.80  
  7 purchase totals = $1,125.56       $1,222.0123   $1,222.03   $1,222.05   $1,222.00