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 $162.70   13.732%   $185.042   $185.04   $185.05   $185.00  
  Purchase #2 $24.36   6.709%   $25.9943   $25.99   $26.00   $26.00  
  Purchase #3 $62.82   4.859%   $65.8724   $65.87   $65.85   $65.90  
  Purchase #4 $163.88   9.268%   $179.0684   $179.07   $179.05   $179.10  
  Purchase #5 $139.82   10.176%   $154.0481   $154.05   $154.05   $154.00  
  Purchase #6 $238.99   6.528%   $254.5913   $254.59   $254.60   $254.60  
  Purchase #7 $245.44   13.445%   $278.4394   $278.44   $278.45   $278.40  
  7 purchase totals = $1,038.01       $1,143.0559   $1,143.05   $1,143.05   $1,143.00