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 $207.40   12.380%   $233.0761   $233.08   $233.10   $233.10  
  Purchase #2 $71.25   13.137%   $80.6101   $80.61   $80.60   $80.60  
  Purchase #3 $9.35   12.236%   $10.4941   $10.49   $10.50   $10.50  
  Purchase #4 $183.86   4.151%   $191.492   $191.49   $191.50   $191.50  
  Purchase #5 $247.53   8.128%   $267.6492   $267.65   $267.65   $267.60  
  Purchase #6 $56.65   6.193%   $60.1583   $60.16   $60.15   $60.20  
  Purchase #7 $22.99   6.327%   $24.4446   $24.44   $24.45   $24.40  
  7 purchase totals = $799.03       $867.9244   $867.92   $867.95   $867.90