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 $214.72   8.151%   $232.2218   $232.22   $232.20   $232.20  
  Purchase #2 $156.26   11.360%   $174.0111   $174.01   $174.00   $174.00  
  Purchase #3 $71.69   5.726%   $75.795   $75.80   $75.80   $75.80  
  Purchase #4 $67.97   5.855%   $71.9496   $71.95   $71.95   $71.90  
  Purchase #5 $27.86   6.129%   $29.5675   $29.57   $29.55   $29.60  
  Purchase #6 $175.70   12.716%   $198.042   $198.04   $198.05   $198.00  
  Purchase #7 $200.36   8.376%   $217.1422   $217.14   $217.15   $217.10  
  7 purchase totals = $914.56       $998.7292   $998.73   $998.70   $998.60