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 $235.43   13.786%   $267.8864   $267.89   $267.90   $267.90  
  Purchase #2 $187.45   11.229%   $208.4988   $208.50   $208.50   $208.50  
  Purchase #3 $8.25   8.422%   $8.9448   $8.94   $8.95   $8.90  
  Purchase #4 $194.96   13.449%   $221.1802   $221.18   $221.20   $221.20  
  Purchase #5 $236.71   8.510%   $256.854   $256.85   $256.85   $256.90  
  Purchase #6 $97.62   7.645%   $105.083   $105.08   $105.10   $105.10  
  Purchase #7 $233.94   10.160%   $257.7083   $257.71   $257.70   $257.70  
  7 purchase totals = $1,194.36       $1,326.1555   $1,326.15   $1,326.20   $1,326.20