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 $44.45   8.569%   $48.2589   $48.26   $48.25   $48.30  
  Purchase #2 $215.70   13.135%   $244.0322   $244.03   $244.05   $244.00  
  Purchase #3 $168.91   3.453%   $174.7425   $174.74   $174.75   $174.70  
  Purchase #4 $214.33   9.152%   $233.9455   $233.95   $233.95   $233.90  
  Purchase #5 $59.38   11.747%   $66.3554   $66.36   $66.35   $66.40  
  Purchase #6 $168.66   10.288%   $186.0117   $186.01   $186.00   $186.00  
  Purchase #7 $22.65   13.838%   $25.7843   $25.78   $25.80   $25.80  
  7 purchase totals = $894.08       $979.1305   $979.13   $979.15   $979.10