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	$150.66	9.717%	$165.2996	$165.30	$165.30	$165.30
Purchase #2	$75.46	3.731%	$78.2754	$78.28	$78.30	$78.30
Purchase #3	$53.64	5.639%	$56.6648	$56.66	$56.65	$56.70
Purchase #4	$250.72	5.562%	$264.665	$264.67	$264.65	$264.70
Purchase #5	$143.77	9.359%	$157.2254	$157.23	$157.25	$157.20
Purchase #6	$32.83	7.529%	$35.3018	$35.30	$35.30	$35.30
Purchase #7	$192.39	11.710%	$214.9189	$214.92	$214.90	$214.90
7 purchase totals =	$899.47		$972.3509	$972.36	$972.35	$972.40