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 $106.63   11.195%   $118.5672   $118.57   $118.55   $118.60  
  Purchase #2 $136.52   13.361%   $154.7604   $154.76   $154.75   $154.80  
  Purchase #3 $72.31   6.437%   $76.9646   $76.96   $76.95   $77.00  
  Purchase #4 $77.86   10.286%   $85.8687   $85.87   $85.85   $85.90  
  Purchase #5 $88.72   6.520%   $94.5045   $94.50   $94.50   $94.50  
  Purchase #6 $161.63   6.387%   $171.9533   $171.95   $171.95   $172.00  
  Purchase #7 $113.89   7.108%   $121.9853   $121.99   $122.00   $122.00  
  7 purchase totals = $757.56       $824.6040   $824.60   $824.55   $824.80