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	$70.74	10.569%	$78.2165	$78.22	$78.20	$78.20
Purchase #2	$30.41	10.459%	$33.5906	$33.59	$33.60	$33.60
Purchase #3	$67.93	5.287%	$71.5215	$71.52	$71.50	$71.50
Purchase #4	$117.95	8.596%	$128.089	$128.09	$128.10	$128.10
Purchase #5	$100.41	12.146%	$112.6058	$112.61	$112.60	$112.60
Purchase #6	$122.85	5.132%	$129.1547	$129.15	$129.15	$129.20
Purchase #7	$60.80	11.124%	$67.5634	$67.56	$67.55	$67.60
7 purchase totals =	$571.09		$620.7415	$620.74	$620.70	$620.80