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	$127.97	13.104%	$144.7392	$144.74	$144.75	$144.70
Purchase #2	$57.86	8.109%	$62.5519	$62.55	$62.55	$62.60
Purchase #3	$246.55	7.301%	$264.5506	$264.55	$264.55	$264.60
Purchase #4	$93.27	6.571%	$99.3988	$99.40	$99.40	$99.40
Purchase #5	$181.39	4.281%	$189.1553	$189.16	$189.15	$189.20
Purchase #6	$79.33	3.369%	$82.0026	$82.00	$82.00	$82.00
Purchase #7	$93.69	12.492%	$105.3938	$105.39	$105.40	$105.40
7 purchase totals =	$880.06		$947.7922	$947.79	$947.80	$947.90