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 $141.81   8.828%   $154.329   $154.33   $154.35   $154.30  
  Purchase #2 $125.25   10.586%   $138.509   $138.51   $138.50   $138.50  
  Purchase #3 $131.76   3.734%   $136.6799   $136.68   $136.70   $136.70  
  Purchase #4 $192.95   5.665%   $203.8806   $203.88   $203.90   $203.90  
  Purchase #5 $218.30   10.615%   $241.4725   $241.47   $241.45   $241.50  
  Purchase #6 $156.57   11.567%   $174.6805   $174.68   $174.70   $174.70  
  Purchase #7 $190.56   12.213%   $213.8331   $213.83   $213.85   $213.80  
  7 purchase totals = $1,157.20       $1,263.3846   $1,263.38   $1,263.45   $1,263.40