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 $66.64   8.617%   $72.3824   $72.38   $72.40   $72.40  
  Purchase #2 $185.95   6.277%   $197.6221   $197.62   $197.60   $197.60  
  Purchase #3 $77.92   11.456%   $86.8465   $86.85   $86.85   $86.80  
  Purchase #4 $175.72   5.346%   $185.114   $185.11   $185.10   $185.10  
  Purchase #5 $56.95   3.578%   $58.9877   $58.99   $59.00   $59.00  
  Purchase #6 $189.46   5.304%   $199.509   $199.51   $199.50   $199.50  
  Purchase #7 $147.85   10.299%   $163.0771   $163.08   $163.10   $163.10  
  7 purchase totals = $900.49       $963.5388   $963.54   $963.55   $963.50