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 $56.87   12.401%   $63.9224   $63.92   $63.90   $63.90  
  Purchase #2 $228.61   9.749%   $250.8972   $250.90   $250.90   $250.90  
  Purchase #3 $12.90   10.167%   $14.2115   $14.21   $14.20   $14.20  
  Purchase #4 $141.34   11.728%   $157.9164   $157.92   $157.90   $157.90  
  Purchase #5 $173.60   11.213%   $193.0658   $193.07   $193.05   $193.10  
  Purchase #6 $60.86   3.163%   $62.785   $62.79   $62.80   $62.80  
  Purchase #7 $242.40   6.151%   $257.31   $257.31   $257.30   $257.30  
  7 purchase totals = $916.58       $1,000.1083   $1,000.12   $1,000.05   $1,000.10