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	$163.90	11.844%	$183.3123	$183.31	$183.30	$183.30
Purchase #2	$240.51	3.316%	$248.4853	$248.49	$248.50	$248.50
Purchase #3	$141.71	11.433%	$157.9117	$157.91	$157.90	$157.90
Purchase #4	$52.30	13.869%	$59.5535	$59.55	$59.55	$59.60
Purchase #5	$240.53	4.471%	$251.2841	$251.28	$251.30	$251.30
Purchase #6	$64.26	12.363%	$72.2045	$72.20	$72.20	$72.20
Purchase #7	$34.41	9.706%	$37.7498	$37.75	$37.75	$37.70
7 purchase totals =	$937.62		$1,010.5012	$1,010.49	$1,010.50	$1,010.50