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 $134.49   12.748%   $151.6348   $151.63   $151.65   $151.60  
  Purchase #2 $233.40   9.588%   $255.7784   $255.78   $255.80   $255.80  
  Purchase #3 $144.42   7.847%   $155.7526   $155.75   $155.75   $155.80  
  Purchase #4 $242.34   5.104%   $254.709   $254.71   $254.70   $254.70  
  Purchase #5 $7.76   3.369%   $8.0214   $8.02   $8.00   $8.00  
  Purchase #6 $183.45   6.397%   $195.1853   $195.19   $195.20   $195.20  
  Purchase #7 $29.40   12.567%   $33.0947   $33.09   $33.10   $33.10  
  7 purchase totals = $975.26       $1,054.1762   $1,054.17   $1,054.20   $1,054.20