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 $7.79   13.149%   $8.8143   $8.81   $8.80   $8.80  
  Purchase #2 $20.47   12.563%   $23.0416   $23.04   $23.05   $23.00  
  Purchase #3 $233.58   13.431%   $264.9521   $264.95   $264.95   $265.00  
  Purchase #4 $102.68   8.485%   $111.3924   $111.39   $111.40   $111.40  
  Purchase #5 $103.49   11.189%   $115.0695   $115.07   $115.05   $115.10  
  Purchase #6 $21.95   13.729%   $24.9635   $24.96   $24.95   $25.00  
  Purchase #7 $152.57   11.862%   $170.6679   $170.67   $170.65   $170.70  
  7 purchase totals = $642.53       $718.9013   $718.89   $718.85   $719.00