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 $144.65   8.806%   $157.3879   $157.39   $157.40   $157.40  
  Purchase #2 $23.77   10.632%   $26.2972   $26.30   $26.30   $26.30  
  Purchase #3 $43.90   7.308%   $47.1082   $47.11   $47.10   $47.10  
  Purchase #4 $234.97   3.704%   $243.6733   $243.67   $243.65   $243.70  
  Purchase #5 $64.33   6.651%   $68.6086   $68.61   $68.60   $68.60  
  Purchase #6 $217.34   9.425%   $237.8243   $237.82   $237.80   $237.80  
  Purchase #7 $215.42   8.282%   $233.2611   $233.26   $233.25   $233.30  
  7 purchase totals = $944.38       $1,014.1606   $1,014.16   $1,014.10   $1,014.20