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 $229.89   7.733%   $247.6674   $247.67   $247.65   $247.70  
  Purchase #2 $63.53   5.687%   $67.143   $67.14   $67.15   $67.10  
  Purchase #3 $45.53   11.166%   $50.6139   $50.61   $50.60   $50.60  
  Purchase #4 $76.27   8.561%   $82.7995   $82.80   $82.80   $82.80  
  Purchase #5 $210.90   11.543%   $235.2442   $235.24   $235.25   $235.20  
  Purchase #6 $103.46   8.525%   $112.28   $112.28   $112.30   $112.30  
  Purchase #7 $30.36   12.836%   $34.257   $34.26   $34.25   $34.30  
  7 purchase totals = $759.94       $830.0050   $830.00   $830.00   $830.00