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 $35.56   3.203%   $36.699   $36.70   $36.70   $36.70  
  Purchase #2 $117.61   7.522%   $126.4566   $126.46   $126.45   $126.50  
  Purchase #3 $176.36   3.484%   $182.5044   $182.50   $182.50   $182.50  
  Purchase #4 $8.72   11.553%   $9.7274   $9.73   $9.75   $9.70  
  Purchase #5 $241.52   7.206%   $258.9239   $258.92   $258.90   $258.90  
  Purchase #6 $90.92   5.691%   $96.0943   $96.09   $96.10   $96.10  
  Purchase #7 $49.67   9.367%   $54.3226   $54.32   $54.30   $54.30  
  7 purchase totals = $720.36       $764.7282   $764.72   $764.70   $764.70