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 $86.81   11.302%   $96.6213   $96.62   $96.60   $96.60  
  Purchase #2 $149.98   6.362%   $159.5217   $159.52   $159.50   $159.50  
  Purchase #3 $98.85   9.514%   $108.2546   $108.25   $108.25   $108.30  
  Purchase #4 $87.86   12.602%   $98.9321   $98.93   $98.95   $98.90  
  Purchase #5 $42.52   11.314%   $47.3307   $47.33   $47.35   $47.30  
  Purchase #6 $234.90   4.230%   $244.8363   $244.84   $244.85   $244.80  
  Purchase #7 $14.81   12.518%   $16.6639   $16.66   $16.65   $16.70  
  7 purchase totals = $715.73       $772.1606   $772.15   $772.15   $772.10