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	$123.75	3.703%	$128.3325	$128.33	$128.35	$128.30
Purchase #2	$184.81	7.399%	$198.4841	$198.48	$198.50	$198.50
Purchase #3	$202.31	4.437%	$211.2865	$211.29	$211.30	$211.30
Purchase #4	$244.83	12.765%	$276.0825	$276.08	$276.10	$276.10
Purchase #5	$103.65	7.658%	$111.5875	$111.59	$111.60	$111.60
Purchase #6	$149.63	3.559%	$154.9553	$154.96	$154.95	$155.00
Purchase #7	$26.38	7.344%	$28.3173	$28.32	$28.30	$28.30
7 purchase totals =	$1,035.36		$1,109.0457	$1,109.05	$1,109.10	$1,109.10