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 $22.41   13.353%   $25.4024   $25.40   $25.40   $25.40  
  Purchase #2 $46.52   10.797%   $51.5428   $51.54   $51.55   $51.50  
  Purchase #3 $159.45   10.165%   $175.6581   $175.66   $175.65   $175.70  
  Purchase #4 $74.49   8.422%   $80.7635   $80.76   $80.75   $80.80  
  Purchase #5 $132.62   9.301%   $144.955   $144.96   $144.95   $145.00  
  Purchase #6 $59.71   12.445%   $67.1409   $67.14   $67.15   $67.10  
  Purchase #7 $161.38   9.805%   $177.2033   $177.20   $177.20   $177.20  
  7 purchase totals = $656.58       $722.6660   $722.66   $722.65   $722.70