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	$73.46	7.733%	$79.1407	$79.14	$79.15	$79.10
Purchase #2	$53.75	9.822%	$59.0293	$59.03	$59.05	$59.00
Purchase #3	$186.64	5.415%	$196.7466	$196.75	$196.75	$196.70
Purchase #4	$86.39	8.104%	$93.391	$93.39	$93.40	$93.40
Purchase #5	$174.83	7.429%	$187.8181	$187.82	$187.80	$187.80
Purchase #6	$174.37	12.424%	$196.0337	$196.03	$196.05	$196.00
Purchase #7	$134.84	10.727%	$149.3043	$149.30	$149.30	$149.30
7 purchase totals =	$884.28		$961.4637	$961.46	$961.50	$961.30