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 $52.39   3.202%   $54.0675   $54.07   $54.05   $54.10  
  Purchase #2 $198.35   9.660%   $217.5106   $217.51   $217.50   $217.50  
  Purchase #3 $151.80   12.610%   $170.942   $170.94   $170.95   $170.90  
  Purchase #4 $156.67   12.215%   $175.8072   $175.81   $175.80   $175.80  
  Purchase #5 $157.26   6.336%   $167.224   $167.22   $167.20   $167.20  
  Purchase #6 $239.44   3.747%   $248.4118   $248.41   $248.40   $248.40  
  Purchase #7 $16.27   11.235%   $18.0979   $18.10   $18.10   $18.10  
  7 purchase totals = $972.18       $1,052.0610   $1,052.06   $1,052.00   $1,052.00