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 $209.86   10.807%   $232.5396   $232.54   $232.55   $232.50  
  Purchase #2 $192.72   6.540%   $205.3239   $205.32   $205.30   $205.30  
  Purchase #3 $141.64   5.598%   $149.569   $149.57   $149.55   $149.60  
  Purchase #4 $234.46   6.353%   $249.3552   $249.36   $249.35   $249.40  
  Purchase #5 $160.46   3.398%   $165.9124   $165.91   $165.90   $165.90  
  Purchase #6 $237.58   10.253%   $261.9391   $261.94   $261.95   $261.90  
  Purchase #7 $211.68   8.707%   $230.111   $230.11   $230.10   $230.10  
  7 purchase totals = $1,388.40       $1,494.7502   $1,494.75   $1,494.70   $1,494.70