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 $92.30   6.774%   $98.5524   $98.55   $98.55   $98.60  
  Purchase #2 $230.57   4.423%   $240.7681   $240.77   $240.75   $240.80  
  Purchase #3 $100.37   7.362%   $107.7592   $107.76   $107.75   $107.80  
  Purchase #4 $242.54   12.663%   $273.2528   $273.25   $273.25   $273.30  
  Purchase #5 $63.47   5.735%   $67.11   $67.11   $67.10   $67.10  
  Purchase #6 $132.42   4.825%   $138.8093   $138.81   $138.80   $138.80  
  Purchase #7 $88.55   9.577%   $97.0304   $97.03   $97.05   $97.00  
  7 purchase totals = $950.22       $1,023.2822   $1,023.28   $1,023.25   $1,023.40