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 $119.70   12.484%   $134.6433   $134.64   $134.65   $134.60  
  Purchase #2 $153.62   8.386%   $166.5026   $166.50   $166.50   $166.50  
  Purchase #3 $245.39   9.789%   $269.4112   $269.41   $269.40   $269.40  
  Purchase #4 $86.67   5.283%   $91.2488   $91.25   $91.25   $91.20  
  Purchase #5 $219.76   8.634%   $238.7341   $238.73   $238.75   $238.70  
  Purchase #6 $7.66   13.137%   $8.6663   $8.67   $8.65   $8.70  
  Purchase #7 $228.92   12.176%   $256.7933   $256.79   $256.80   $256.80  
  7 purchase totals = $1,061.72       $1,165.9996   $1,165.99   $1,166.00   $1,165.90