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 $41.66   6.425%   $44.3367   $44.34   $44.35   $44.30  
  Purchase #2 $61.83   12.452%   $69.5291   $69.53   $69.55   $69.50  
  Purchase #3 $232.98   9.609%   $255.367   $255.37   $255.35   $255.40  
  Purchase #4 $8.69   8.339%   $9.4147   $9.41   $9.40   $9.40  
  Purchase #5 $196.90   9.536%   $215.6764   $215.68   $215.70   $215.70  
  Purchase #6 $249.25   13.753%   $283.5294   $283.53   $283.55   $283.50  
  Purchase #7 $6.35   11.207%   $7.0616   $7.06   $7.05   $7.10  
  7 purchase totals = $797.66       $884.9149   $884.92   $884.95   $884.90