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	$51.92	5.802%	$54.9324	$54.93	$54.95	$54.90
Purchase #2	$221.36	3.466%	$229.0323	$229.03	$229.05	$229.00
Purchase #3	$129.44	5.782%	$136.9242	$136.92	$136.90	$136.90
Purchase #4	$42.53	9.779%	$46.689	$46.69	$46.70	$46.70
Purchase #5	$243.86	13.479%	$276.7299	$276.73	$276.75	$276.70
Purchase #6	$88.74	13.286%	$100.53	$100.53	$100.55	$100.50
Purchase #7	$40.35	13.407%	$45.7597	$45.76	$45.75	$45.80
7 purchase totals =	$818.20		$890.5975	$890.59	$890.65	$890.50