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	$233.46	6.738%	$249.1905	$249.19	$249.20	$249.20
Purchase #2	$136.35	7.634%	$146.759	$146.76	$146.75	$146.80
Purchase #3	$227.31	4.565%	$237.6867	$237.69	$237.70	$237.70
Purchase #4	$129.48	4.315%	$135.0671	$135.07	$135.05	$135.10
Purchase #5	$169.56	12.612%	$190.9449	$190.94	$190.95	$190.90
Purchase #6	$186.49	5.440%	$196.6351	$196.64	$196.65	$196.60
Purchase #7	$89.54	10.854%	$99.2587	$99.26	$99.25	$99.30
7 purchase totals =	$1,172.19		$1,255.5420	$1,255.55	$1,255.55	$1,255.60