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 $162.87   6.448%   $173.3719   $173.37   $173.35   $173.40  
  Purchase #2 $178.84   5.555%   $188.7746   $188.77   $188.75   $188.80  
  Purchase #3 $23.85   4.769%   $24.9874   $24.99   $25.00   $25.00  
  Purchase #4 $233.98   6.781%   $249.8462   $249.85   $249.85   $249.80  
  Purchase #5 $202.38   6.778%   $216.0973   $216.10   $216.10   $216.10  
  Purchase #6 $68.57   11.333%   $76.341   $76.34   $76.35   $76.30  
  Purchase #7 $97.99   6.353%   $104.2153   $104.22   $104.20   $104.20  
  7 purchase totals = $968.48       $1,033.6337   $1,033.64   $1,033.60   $1,033.60