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 $75.95   10.277%   $83.7554   $83.76   $83.75   $83.80  
  Purchase #2 $119.41   6.113%   $126.7095   $126.71   $126.70   $126.70  
  Purchase #3 $169.49   6.785%   $180.9899   $180.99   $181.00   $181.00  
  Purchase #4 $61.49   8.301%   $66.5943   $66.59   $66.60   $66.60  
  Purchase #5 $76.53   13.204%   $86.635   $86.64   $86.65   $86.60  
  Purchase #6 $16.67   12.694%   $18.7861   $18.79   $18.80   $18.80  
  Purchase #7 $123.49   5.739%   $130.5771   $130.58   $130.60   $130.60  
  7 purchase totals = $643.03       $694.0473   $694.06   $694.10   $694.10