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 $226.91   8.622%   $246.4742   $246.47   $246.45   $246.50  
  Purchase #2 $189.63   4.232%   $197.6551   $197.66   $197.65   $197.70  
  Purchase #3 $44.60   3.184%   $46.0201   $46.02   $46.00   $46.00  
  Purchase #4 $48.41   4.677%   $50.6741   $50.67   $50.65   $50.70  
  Purchase #5 $25.54   8.196%   $27.6333   $27.63   $27.65   $27.60  
  Purchase #6 $123.58   3.378%   $127.7545   $127.75   $127.75   $127.80  
  Purchase #7 $176.92   12.774%   $199.5198   $199.52   $199.50   $199.50  
  7 purchase totals = $835.59       $895.7311   $895.72   $895.65   $895.80