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	$56.63	12.617%	$63.775	$63.78	$63.80	$63.80
Purchase #2	$207.36	4.498%	$216.6871	$216.69	$216.70	$216.70
Purchase #3	$72.30	7.132%	$77.4564	$77.46	$77.45	$77.50
Purchase #4	$112.94	9.414%	$123.5722	$123.57	$123.55	$123.60
Purchase #5	$38.61	7.414%	$41.4725	$41.47	$41.45	$41.50
Purchase #6	$249.90	7.767%	$269.3097	$269.31	$269.30	$269.30
Purchase #7	$54.77	13.228%	$62.015	$62.02	$62.00	$62.00
7 purchase totals =	$792.51		$854.2879	$854.30	$854.25	$854.40