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 $204.80   13.767%   $232.9948   $232.99   $233.00   $233.00  
  Purchase #2 $38.55   10.783%   $42.7068   $42.71   $42.70   $42.70  
  Purchase #3 $156.72   12.395%   $176.1454   $176.15   $176.15   $176.10  
  Purchase #4 $94.49   6.865%   $100.9767   $100.98   $101.00   $101.00  
  Purchase #5 $78.66   8.840%   $85.6135   $85.61   $85.60   $85.60  
  Purchase #6 $29.87   8.393%   $32.377   $32.38   $32.40   $32.40  
  Purchase #7 $213.56   10.349%   $235.6613   $235.66   $235.65   $235.70  
  7 purchase totals = $816.65       $906.4755   $906.48   $906.50   $906.50