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	$229.87	4.789%	$240.8785	$240.88	$240.90	$240.90
Purchase #2	$171.68	4.390%	$179.2168	$179.22	$179.20	$179.20
Purchase #3	$185.96	5.700%	$196.5597	$196.56	$196.55	$196.60
Purchase #4	$193.37	8.580%	$209.9611	$209.96	$209.95	$210.00
Purchase #5	$51.96	4.656%	$54.3793	$54.38	$54.40	$54.40
Purchase #6	$71.90	7.248%	$77.1113	$77.11	$77.10	$77.10
Purchase #7	$22.57	4.289%	$23.538	$23.54	$23.55	$23.50
7 purchase totals =	$927.31		$981.6447	$981.65	$981.65	$981.70