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 $76.61   6.732%   $81.7674   $81.77   $81.75   $81.80  
  Purchase #2 $151.32   3.471%   $156.5723   $156.57   $156.55   $156.60  
  Purchase #3 $38.91   3.224%   $40.1645   $40.16   $40.15   $40.20  
  Purchase #4 $241.49   10.455%   $266.7378   $266.74   $266.75   $266.70  
  Purchase #5 $27.39   13.615%   $31.1191   $31.12   $31.10   $31.10  
  Purchase #6 $146.60   4.441%   $153.1105   $153.11   $153.10   $153.10  
  Purchase #7 $203.33   11.741%   $227.203   $227.20   $227.20   $227.20  
  7 purchase totals = $885.65       $956.6746   $956.67   $956.60   $956.70