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	$64.63	10.307%	$71.2914	$71.29	$71.30	$71.30
Purchase #2	$62.98	11.299%	$70.0961	$70.10	$70.10	$70.10
Purchase #3	$170.95	11.159%	$190.0263	$190.03	$190.05	$190.00
Purchase #4	$202.36	9.630%	$221.8473	$221.85	$221.85	$221.80
Purchase #5	$191.39	9.743%	$210.0371	$210.04	$210.05	$210.00
Purchase #6	$149.42	4.500%	$156.1439	$156.14	$156.15	$156.10
Purchase #7	$83.67	11.743%	$93.4954	$93.50	$93.50	$93.50
7 purchase totals =	$925.40		$1,012.9375	$1,012.95	$1,013.00	$1,012.80