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 $113.44   4.159%   $118.158   $118.16   $118.15   $118.20  
  Purchase #2 $75.90   7.226%   $81.3845   $81.38   $81.40   $81.40  
  Purchase #3 $167.51   9.463%   $183.3615   $183.36   $183.35   $183.40  
  Purchase #4 $34.42   5.616%   $36.353   $36.35   $36.35   $36.40  
  Purchase #5 $244.44   11.867%   $273.4477   $273.45   $273.45   $273.40  
  Purchase #6 $11.64   11.806%   $13.0142   $13.01   $13.00   $13.00  
  Purchase #7 $59.44   3.732%   $61.6583   $61.66   $61.65   $61.70  
  7 purchase totals = $706.79       $767.3772   $767.37   $767.35   $767.50