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 $88.72   10.184%   $97.7552   $97.76   $97.75   $97.80  
  Purchase #2 $90.65   8.313%   $98.1857   $98.19   $98.20   $98.20  
  Purchase #3 $64.64   9.797%   $70.9728   $70.97   $70.95   $71.00  
  Purchase #4 $36.52   4.611%   $38.2039   $38.20   $38.20   $38.20  
  Purchase #5 $93.69   4.232%   $97.655   $97.66   $97.65   $97.70  
  Purchase #6 $50.36   4.410%   $52.5809   $52.58   $52.60   $52.60  
  Purchase #7 $55.63   11.335%   $61.9357   $61.94   $61.95   $61.90  
  7 purchase totals = $480.21       $517.2892   $517.30   $517.30   $517.40