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 $127.94   13.138%   $144.7488   $144.75   $144.75   $144.70  
  Purchase #2 $82.44   12.357%   $92.6271   $92.63   $92.65   $92.60  
  Purchase #3 $94.26   4.564%   $98.562   $98.56   $98.55   $98.60  
  Purchase #4 $247.36   13.718%   $281.2928   $281.29   $281.30   $281.30  
  Purchase #5 $192.96   9.459%   $211.2121   $211.21   $211.20   $211.20  
  Purchase #6 $190.53   4.648%   $199.3858   $199.39   $199.40   $199.40  
  Purchase #7 $22.61   4.393%   $23.6033   $23.60   $23.60   $23.60  
  7 purchase totals = $958.10       $1,051.4319   $1,051.43   $1,051.45   $1,051.40