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 $149.26   12.315%   $167.6414   $167.64   $167.65   $167.60  
  Purchase #2 $199.75   8.836%   $217.3999   $217.40   $217.40   $217.40  
  Purchase #3 $12.66   5.176%   $13.3153   $13.32   $13.30   $13.30  
  Purchase #4 $221.59   10.716%   $245.3356   $245.34   $245.35   $245.30  
  Purchase #5 $72.27   7.246%   $77.5067   $77.51   $77.50   $77.50  
  Purchase #6 $166.26   6.230%   $176.618   $176.62   $176.60   $176.60  
  Purchase #7 $249.52   7.469%   $268.1566   $268.16   $268.15   $268.20  
  7 purchase totals = $1,071.31       $1,165.9735   $1,165.99   $1,165.95   $1,165.90