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 $32.45   6.680%   $34.6177   $34.62   $34.60   $34.60  
  Purchase #2 $24.26   4.664%   $25.3915   $25.39   $25.40   $25.40  
  Purchase #3 $61.34   5.708%   $64.8413   $64.84   $64.85   $64.80  
  Purchase #4 $202.70   11.332%   $225.67   $225.67   $225.65   $225.70  
  Purchase #5 $85.87   3.135%   $88.562   $88.56   $88.55   $88.60  
  Purchase #6 $178.95   7.236%   $191.8988   $191.90   $191.90   $191.90  
  Purchase #7 $235.70   6.779%   $251.6781   $251.68   $251.70   $251.70  
  7 purchase totals = $821.27       $882.6594   $882.66   $882.65   $882.70