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 $228.96   8.131%   $247.5767   $247.58   $247.60   $247.60  
  Purchase #2 $7.42   6.344%   $7.8907   $7.89   $7.90   $7.90  
  Purchase #3 $69.87   10.654%   $77.3139   $77.31   $77.30   $77.30  
  Purchase #4 $86.36   7.150%   $92.5347   $92.53   $92.55   $92.50  
  Purchase #5 $196.81   8.337%   $213.218   $213.22   $213.20   $213.20  
  Purchase #6 $79.26   8.824%   $86.2539   $86.25   $86.25   $86.30  
  Purchase #7 $216.38   4.196%   $225.4593   $225.46   $225.45   $225.50  
  7 purchase totals = $885.06       $950.2472   $950.24   $950.25   $950.30