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 $53.92   7.310%   $57.8616   $57.86   $57.85   $57.90  
  Purchase #2 $34.42   12.284%   $38.6482   $38.65   $38.65   $38.60  
  Purchase #3 $177.81   11.329%   $197.9541   $197.95   $197.95   $198.00  
  Purchase #4 $95.94   4.474%   $100.2324   $100.23   $100.25   $100.20  
  Purchase #5 $235.68   10.186%   $259.6864   $259.69   $259.70   $259.70  
  Purchase #6 $231.26   11.307%   $257.4086   $257.41   $257.40   $257.40  
  Purchase #7 $202.40   8.517%   $219.6384   $219.64   $219.65   $219.60  
  7 purchase totals = $1,031.43       $1,131.4297   $1,131.43   $1,131.45   $1,131.40