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 $154.86   9.620%   $169.7575   $169.76   $169.75   $169.80  
  Purchase #2 $209.67   4.147%   $218.365   $218.37   $218.35   $218.40  
  Purchase #3 $231.91   12.766%   $261.5156   $261.52   $261.50   $261.50  
  Purchase #4 $61.87   6.472%   $65.8742   $65.87   $65.85   $65.90  
  Purchase #5 $177.46   8.752%   $192.9913   $192.99   $193.00   $193.00  
  Purchase #6 $156.82   7.616%   $168.7634   $168.76   $168.75   $168.80  
  Purchase #7 $88.36   4.543%   $92.3742   $92.37   $92.35   $92.40  
  7 purchase totals = $1,080.95       $1,169.6412   $1,169.64   $1,169.55   $1,169.80