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 $21.54   9.127%   $23.506   $23.51   $23.50   $23.50  
  Purchase #2 $44.81   5.478%   $47.2647   $47.26   $47.25   $47.30  
  Purchase #3 $39.82   12.227%   $44.6888   $44.69   $44.70   $44.70  
  Purchase #4 $33.80   3.264%   $34.9032   $34.90   $34.90   $34.90  
  Purchase #5 $211.53   10.422%   $233.5757   $233.58   $233.60   $233.60  
  Purchase #6 $148.87   12.269%   $167.1349   $167.13   $167.15   $167.10  
  Purchase #7 $204.52   6.661%   $218.1431   $218.14   $218.15   $218.10  
  7 purchase totals = $704.89       $769.2164   $769.21   $769.25   $769.20