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 $157.74   11.665%   $176.1404   $176.14   $176.15   $176.10  
  Purchase #2 $248.40   12.197%   $278.6973   $278.70   $278.70   $278.70  
  Purchase #3 $33.28   4.868%   $34.9001   $34.90   $34.90   $34.90  
  Purchase #4 $160.48   12.315%   $180.2431   $180.24   $180.25   $180.20  
  Purchase #5 $66.84   6.415%   $71.1278   $71.13   $71.15   $71.10  
  Purchase #6 $111.25   13.830%   $126.6359   $126.64   $126.65   $126.60  
  Purchase #7 $84.50   8.385%   $91.5853   $91.59   $91.60   $91.60  
  7 purchase totals = $862.49       $959.3299   $959.34   $959.40   $959.20