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 $66.84   12.139%   $74.9537   $74.95   $74.95   $75.00  
  Purchase #2 $49.80   13.151%   $56.3492   $56.35   $56.35   $56.30  
  Purchase #3 $60.86   8.109%   $65.7951   $65.80   $65.80   $65.80  
  Purchase #4 $157.38   9.122%   $171.7362   $171.74   $171.75   $171.70  
  Purchase #5 $233.60   13.473%   $265.0729   $265.07   $265.05   $265.10  
  Purchase #6 $123.48   13.463%   $140.1041   $140.10   $140.10   $140.10  
  Purchase #7 $115.66   9.796%   $126.9901   $126.99   $127.00   $127.00  
  7 purchase totals = $807.62       $901.0013   $901.00   $901.00   $901.00