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 $110.54   13.858%   $125.8586   $125.86   $125.85   $125.90  
  Purchase #2 $6.92   9.662%   $7.5886   $7.59   $7.60   $7.60  
  Purchase #3 $80.58   8.695%   $87.5864   $87.59   $87.60   $87.60  
  Purchase #4 $213.49   7.452%   $229.3993   $229.40   $229.40   $229.40  
  Purchase #5 $236.35   4.492%   $246.9668   $246.97   $246.95   $247.00  
  Purchase #6 $89.80   3.383%   $92.8379   $92.84   $92.85   $92.80  
  Purchase #7 $13.35   7.673%   $14.3743   $14.37   $14.35   $14.40  
  7 purchase totals = $751.03       $804.6119   $804.62   $804.60   $804.70