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 $85.72   13.577%   $97.3582   $97.36   $97.35   $97.40  
  Purchase #2 $71.89   4.334%   $75.0057   $75.01   $75.00   $75.00  
  Purchase #3 $212.27   10.474%   $234.5032   $234.50   $234.50   $234.50  
  Purchase #4 $170.29   9.688%   $186.7877   $186.79   $186.80   $186.80  
  Purchase #5 $53.87   11.169%   $59.8867   $59.89   $59.90   $59.90  
  Purchase #6 $219.38   6.769%   $234.2298   $234.23   $234.25   $234.20  
  Purchase #7 $53.98   4.285%   $56.293   $56.29   $56.30   $56.30  
  7 purchase totals = $867.40       $944.0643   $944.07   $944.10   $944.10