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 $207.88   13.763%   $236.4905   $236.49   $236.50   $236.50  
  Purchase #2 $133.94   5.750%   $141.6416   $141.64   $141.65   $141.60  
  Purchase #3 $46.31   7.770%   $49.9083   $49.91   $49.90   $49.90  
  Purchase #4 $115.88   7.170%   $124.1886   $124.19   $124.20   $124.20  
  Purchase #5 $66.46   6.798%   $70.978   $70.98   $71.00   $71.00  
  Purchase #6 $31.77   12.438%   $35.7216   $35.72   $35.70   $35.70  
  Purchase #7 $99.51   13.662%   $113.1051   $113.11   $113.10   $113.10  
  7 purchase totals = $701.75       $772.0337   $772.04   $772.05   $772.00