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 $62.32   4.705%   $65.2522   $65.25   $65.25   $65.30  
  Purchase #2 $24.34   6.222%   $25.8544   $25.85   $25.85   $25.90  
  Purchase #3 $39.78   13.360%   $45.0946   $45.09   $45.10   $45.10  
  Purchase #4 $131.83   10.396%   $145.535   $145.54   $145.55   $145.50  
  Purchase #5 $193.85   6.740%   $206.9155   $206.92   $206.90   $206.90  
  Purchase #6 $101.99   11.188%   $113.4006   $113.40   $113.40   $113.40  
  Purchase #7 $162.60   8.216%   $175.9592   $175.96   $175.95   $176.00  
  7 purchase totals = $716.71       $778.0115   $778.01   $778.00   $778.10