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 $209.36   8.274%   $226.6824   $226.68   $226.70   $226.70  
  Purchase #2 $223.52   4.646%   $233.9047   $233.90   $233.90   $233.90  
  Purchase #3 $6.37   10.557%   $7.0425   $7.04   $7.05   $7.00  
  Purchase #4 $175.59   6.874%   $187.6601   $187.66   $187.65   $187.70  
  Purchase #5 $190.82   13.116%   $215.848   $215.85   $215.85   $215.80  
  Purchase #6 $99.68   13.429%   $113.066   $113.07   $113.05   $113.10  
  Purchase #7 $112.79   11.666%   $125.9481   $125.95   $125.95   $125.90  
  7 purchase totals = $1,018.13       $1,110.1518   $1,110.15   $1,110.15   $1,110.10