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 $38.92   5.381%   $41.0143   $41.01   $41.00   $41.00  
  Purchase #2 $125.79   13.652%   $142.9629   $142.96   $142.95   $143.00  
  Purchase #3 $129.77   5.234%   $136.5622   $136.56   $136.55   $136.60  
  Purchase #4 $165.83   10.104%   $182.5855   $182.59   $182.60   $182.60  
  Purchase #5 $135.90   9.211%   $148.4177   $148.42   $148.40   $148.40  
  Purchase #6 $117.42   4.565%   $122.7802   $122.78   $122.80   $122.80  
  Purchase #7 $243.62   9.364%   $266.4326   $266.43   $266.45   $266.40  
  7 purchase totals = $957.25       $1,040.7554   $1,040.75   $1,040.75   $1,040.80