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 $156.83   13.206%   $177.541   $177.54   $177.55   $177.50  
  Purchase #2 $5.55   4.733%   $5.8127   $5.81   $5.80   $5.80  
  Purchase #3 $195.51   8.380%   $211.8937   $211.89   $211.90   $211.90  
  Purchase #4 $68.77   9.539%   $75.33   $75.33   $75.35   $75.30  
  Purchase #5 $202.79   5.306%   $213.55   $213.55   $213.55   $213.60  
  Purchase #6 $179.71   9.772%   $197.2713   $197.27   $197.25   $197.30  
  Purchase #7 $81.27   4.116%   $84.6151   $84.62   $84.60   $84.60  
  7 purchase totals = $890.43       $966.0138   $966.01   $966.00   $966.00