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 $232.87   5.554%   $245.8036   $245.80   $245.80   $245.80  
  Purchase #2 $88.40   5.429%   $93.1992   $93.20   $93.20   $93.20  
  Purchase #3 $137.68   10.477%   $152.1047   $152.10   $152.10   $152.10  
  Purchase #4 $186.25   6.141%   $197.6876   $197.69   $197.70   $197.70  
  Purchase #5 $157.95   12.863%   $178.2671   $178.27   $178.25   $178.30  
  Purchase #6 $9.51   7.248%   $10.1993   $10.20   $10.20   $10.20  
  Purchase #7 $120.66   3.229%   $124.5561   $124.56   $124.55   $124.60  
  7 purchase totals = $933.32       $1,001.8176   $1,001.82   $1,001.80   $1,001.90