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	$243.46	10.124%	$268.1079	$268.11	$268.10	$268.10
Purchase #2	$179.36	6.766%	$191.4955	$191.50	$191.50	$191.50
Purchase #3	$100.26	11.362%	$111.6515	$111.65	$111.65	$111.70
Purchase #4	$218.99	4.167%	$228.1153	$228.12	$228.10	$228.10
Purchase #5	$142.71	3.413%	$147.5807	$147.58	$147.60	$147.60
Purchase #6	$214.39	10.776%	$237.4927	$237.49	$237.50	$237.50
Purchase #7	$204.31	8.819%	$222.3281	$222.33	$222.35	$222.30
7 purchase totals =	$1,303.48		$1,406.7717	$1,406.78	$1,406.80	$1,406.80