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 $56.43   6.675%   $60.1967   $60.20   $60.20   $60.20  
  Purchase #2 $235.43   6.106%   $249.8054   $249.81   $249.80   $249.80  
  Purchase #3 $46.68   7.813%   $50.3271   $50.33   $50.35   $50.30  
  Purchase #4 $223.57   11.369%   $248.9877   $248.99   $249.00   $249.00  
  Purchase #5 $50.93   12.571%   $57.3324   $57.33   $57.35   $57.30  
  Purchase #6 $217.33   6.296%   $231.0131   $231.01   $231.00   $231.00  
  Purchase #7 $210.54   3.874%   $218.6963   $218.70   $218.70   $218.70  
  7 purchase totals = $1,040.91       $1,116.3587   $1,116.37   $1,116.40   $1,116.30