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	$189.41	13.567%	$215.1073	$215.11	$215.10	$215.10
Purchase #2	$158.55	12.153%	$177.8186	$177.82	$177.80	$177.80
Purchase #3	$90.34	12.303%	$101.4545	$101.45	$101.45	$101.50
Purchase #4	$114.39	13.210%	$129.5009	$129.50	$129.50	$129.50
Purchase #5	$149.41	4.335%	$155.8869	$155.89	$155.90	$155.90
Purchase #6	$84.30	6.127%	$89.4651	$89.47	$89.45	$89.50
Purchase #7	$250.95	9.729%	$275.3649	$275.36	$275.35	$275.40
7 purchase totals =	$1,037.35		$1,144.5982	$1,144.60	$1,144.55	$1,144.70