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 $60.41   8.403%   $65.4863   $65.49   $65.50   $65.50  
  Purchase #2 $160.78   4.656%   $168.2659   $168.27   $168.25   $168.30  
  Purchase #3 $190.32   3.866%   $197.6778   $197.68   $197.70   $197.70  
  Purchase #4 $153.94   9.557%   $168.652   $168.65   $168.65   $168.70  
  Purchase #5 $166.30   9.366%   $181.8757   $181.88   $181.90   $181.90  
  Purchase #6 $63.27   5.848%   $66.97   $66.97   $66.95   $67.00  
  Purchase #7 $16.76   11.286%   $18.6515   $18.65   $18.65   $18.70  
  7 purchase totals = $811.78       $867.5792   $867.59   $867.60   $867.80