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 $46.26   11.308%   $51.4911   $51.49   $51.50   $51.50  
  Purchase #2 $246.44   6.649%   $262.8258   $262.83   $262.85   $262.80  
  Purchase #3 $144.96   6.436%   $154.2896   $154.29   $154.30   $154.30  
  Purchase #4 $227.46   8.673%   $247.1876   $247.19   $247.20   $247.20  
  Purchase #5 $238.34   10.445%   $263.2346   $263.23   $263.25   $263.20  
  Purchase #6 $186.29   4.229%   $194.1682   $194.17   $194.15   $194.20  
  Purchase #7 $88.51   5.681%   $93.5383   $93.54   $93.55   $93.50  
  7 purchase totals = $1,178.26       $1,266.7352   $1,266.74   $1,266.80   $1,266.70