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 $62.49   6.605%   $66.6175   $66.62   $66.60   $66.60  
  Purchase #2 $148.29   7.249%   $159.0395   $159.04   $159.05   $159.00  
  Purchase #3 $242.43   4.226%   $252.6751   $252.68   $252.70   $252.70  
  Purchase #4 $131.50   3.354%   $135.9105   $135.91   $135.90   $135.90  
  Purchase #5 $86.46   3.109%   $89.148   $89.15   $89.15   $89.10  
  Purchase #6 $233.62   5.669%   $246.8639   $246.86   $246.85   $246.90  
  Purchase #7 $63.35   3.106%   $65.3177   $65.32   $65.30   $65.30  
  7 purchase totals = $968.14       $1,015.5722   $1,015.58   $1,015.55   $1,015.50