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 $76.51   8.874%   $83.2995   $83.30   $83.30   $83.30  
  Purchase #2 $49.98   12.716%   $56.3355   $56.34   $56.35   $56.30  
  Purchase #3 $230.65   3.683%   $239.1448   $239.14   $239.15   $239.10  
  Purchase #4 $20.36   5.650%   $21.5103   $21.51   $21.50   $21.50  
  Purchase #5 $223.91   7.845%   $241.4757   $241.48   $241.50   $241.50  
  Purchase #6 $115.30   3.192%   $118.9804   $118.98   $119.00   $119.00  
  Purchase #7 $148.80   10.396%   $164.2692   $164.27   $164.25   $164.30  
  7 purchase totals = $865.51       $925.0154   $925.02   $925.05   $925.00