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 $241.78   10.716%   $267.6891   $267.69   $267.70   $267.70  
  Purchase #2 $182.36   12.374%   $204.9252   $204.93   $204.95   $204.90  
  Purchase #3 $130.97   7.697%   $141.0508   $141.05   $141.05   $141.10  
  Purchase #4 $165.98   4.865%   $174.0549   $174.05   $174.05   $174.10  
  Purchase #5 $22.80   8.348%   $24.7033   $24.70   $24.70   $24.70  
  Purchase #6 $158.77   4.777%   $166.3544   $166.35   $166.35   $166.40  
  Purchase #7 $7.64   12.212%   $8.573   $8.57   $8.55   $8.60  
  7 purchase totals = $910.30       $987.3507   $987.34   $987.35   $987.50