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 $178.58   13.461%   $202.6187   $202.62   $202.60   $202.60  
  Purchase #2 $232.66   6.562%   $247.9271   $247.93   $247.95   $247.90  
  Purchase #3 $250.31   4.827%   $262.3925   $262.39   $262.40   $262.40  
  Purchase #4 $185.27   11.631%   $206.8188   $206.82   $206.80   $206.80  
  Purchase #5 $26.92   5.448%   $28.3866   $28.39   $28.40   $28.40  
  Purchase #6 $17.54   11.321%   $19.5257   $19.53   $19.55   $19.50  
  Purchase #7 $81.75   5.338%   $86.1138   $86.11   $86.10   $86.10  
  7 purchase totals = $973.03       $1,053.7832   $1,053.79   $1,053.80   $1,053.70