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 $66.54   4.451%   $69.5017   $69.50   $69.50   $69.50  
  Purchase #2 $99.45   11.469%   $110.8559   $110.86   $110.85   $110.90  
  Purchase #3 $202.47   5.873%   $214.3611   $214.36   $214.35   $214.40  
  Purchase #4 $62.40   11.481%   $69.5641   $69.56   $69.55   $69.60  
  Purchase #5 $167.95   5.729%   $177.5719   $177.57   $177.55   $177.60  
  Purchase #6 $107.27   13.256%   $121.4897   $121.49   $121.50   $121.50  
  Purchase #7 $173.54   10.837%   $192.3465   $192.35   $192.35   $192.30  
  7 purchase totals = $879.62       $955.6909   $955.69   $955.65   $955.80