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 $211.41   11.290%   $235.2782   $235.28   $235.30   $235.30  
  Purchase #2 $247.52   9.630%   $271.3562   $271.36   $271.35   $271.40  
  Purchase #3 $34.49   12.319%   $38.7388   $38.74   $38.75   $38.70  
  Purchase #4 $221.31   10.512%   $244.5741   $244.57   $244.55   $244.60  
  Purchase #5 $23.88   6.388%   $25.4055   $25.41   $25.40   $25.40  
  Purchase #6 $59.29   3.109%   $61.1333   $61.13   $61.15   $61.10  
  Purchase #7 $50.40   13.105%   $57.0049   $57.00   $57.00   $57.00  
  7 purchase totals = $848.30       $933.4910   $933.49   $933.50   $933.50