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	$48.85	13.445%	$55.4179	$55.42	$55.40	$55.40
Purchase #2	$44.45	13.710%	$50.5441	$50.54	$50.55	$50.50
Purchase #3	$206.32	3.180%	$212.881	$212.88	$212.90	$212.90
Purchase #4	$145.92	7.298%	$156.5692	$156.57	$156.55	$156.60
Purchase #5	$177.53	10.759%	$196.6305	$196.63	$196.65	$196.60
Purchase #6	$214.40	4.420%	$223.8765	$223.88	$223.90	$223.90
Purchase #7	$217.72	8.179%	$235.5273	$235.53	$235.55	$235.50
7 purchase totals =	$1,055.19		$1,131.4465	$1,131.45	$1,131.50	$1,131.40