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	$5.78	4.231%	$6.0246	$6.02	$6.00	$6.00
Purchase #2	$230.63	6.473%	$245.5587	$245.56	$245.55	$245.60
Purchase #3	$48.83	8.119%	$52.7945	$52.79	$52.80	$52.80
Purchase #4	$60.51	3.297%	$62.505	$62.51	$62.50	$62.50
Purchase #5	$62.50	13.253%	$70.7831	$70.78	$70.80	$70.80
Purchase #6	$91.75	7.399%	$98.5386	$98.54	$98.55	$98.50
Purchase #7	$88.27	12.358%	$99.1784	$99.18	$99.20	$99.20
7 purchase totals =	$588.27		$635.3829	$635.38	$635.40	$635.40