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	$226.27	12.803%	$255.2393	$255.24	$255.25	$255.20
Purchase #2	$135.46	7.835%	$146.0733	$146.07	$146.05	$146.10
Purchase #3	$178.53	6.814%	$190.695	$190.70	$190.70	$190.70
Purchase #4	$79.53	12.461%	$89.4402	$89.44	$89.45	$89.40
Purchase #5	$194.64	6.547%	$207.3831	$207.38	$207.40	$207.40
Purchase #6	$45.40	12.686%	$51.1594	$51.16	$51.15	$51.20
Purchase #7	$32.61	4.109%	$33.9499	$33.95	$33.95	$33.90
7 purchase totals =	$892.44		$973.9402	$973.94	$973.95	$973.90