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	$90.73	13.503%	$102.9813	$102.98	$103.00	$103.00
Purchase #2	$77.86	13.526%	$88.3913	$88.39	$88.40	$88.40
Purchase #3	$37.87	11.823%	$42.3474	$42.35	$42.35	$42.30
Purchase #4	$124.83	9.523%	$136.7176	$136.72	$136.70	$136.70
Purchase #5	$48.45	3.593%	$50.1908	$50.19	$50.20	$50.20
Purchase #6	$53.97	4.270%	$56.2745	$56.27	$56.25	$56.30
Purchase #7	$243.89	8.474%	$264.5572	$264.56	$264.55	$264.60
7 purchase totals =	$677.60		$741.4601	$741.46	$741.45	$741.50