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 $164.32   12.383%   $184.6677   $184.67   $184.65   $184.70  
  Purchase #2 $43.90   10.474%   $48.4981   $48.50   $48.50   $48.50  
  Purchase #3 $119.29   8.561%   $129.5024   $129.50   $129.50   $129.50  
  Purchase #4 $141.46   13.393%   $160.4057   $160.41   $160.40   $160.40  
  Purchase #5 $209.70   7.807%   $226.0713   $226.07   $226.05   $226.10  
  Purchase #6 $124.44   8.139%   $134.5682   $134.57   $134.55   $134.60  
  Purchase #7 $134.91   4.613%   $141.1334   $141.13   $141.15   $141.10  
  7 purchase totals = $938.02       $1,024.8468   $1,024.85   $1,024.80   $1,024.90