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 $84.61   8.312%   $91.6428   $91.64   $91.65   $91.60  
  Purchase #2 $133.39   8.370%   $144.5547   $144.55   $144.55   $144.60  
  Purchase #3 $51.77   12.169%   $58.0699   $58.07   $58.05   $58.10  
  Purchase #4 $233.96   3.217%   $241.4865   $241.49   $241.50   $241.50  
  Purchase #5 $145.96   11.436%   $162.652   $162.65   $162.65   $162.70  
  Purchase #6 $239.40   3.218%   $247.1039   $247.10   $247.10   $247.10  
  Purchase #7 $103.87   3.633%   $107.6436   $107.64   $107.65   $107.60  
  7 purchase totals = $992.96       $1,053.1534   $1,053.14   $1,053.15   $1,053.20