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 $246.48   12.393%   $277.0263   $277.03   $277.05   $277.00  
  Purchase #2 $94.51   11.163%   $105.0602   $105.06   $105.05   $105.10  
  Purchase #3 $183.83   4.678%   $192.4296   $192.43   $192.45   $192.40  
  Purchase #4 $89.92   9.677%   $98.6216   $98.62   $98.60   $98.60  
  Purchase #5 $207.82   8.503%   $225.4909   $225.49   $225.50   $225.50  
  Purchase #6 $66.70   12.625%   $75.1209   $75.12   $75.10   $75.10  
  Purchase #7 $26.39   4.334%   $27.5337   $27.53   $27.55   $27.50  
  7 purchase totals = $915.65       $1,001.2832   $1,001.28   $1,001.30   $1,001.20