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	$204.88	12.173%	$229.82	$229.82	$229.80	$229.80
Purchase #2	$66.42	6.800%	$70.9366	$70.94	$70.95	$70.90
Purchase #3	$87.52	3.858%	$90.8965	$90.90	$90.90	$90.90
Purchase #4	$31.92	9.838%	$35.0603	$35.06	$35.05	$35.10
Purchase #5	$240.31	12.676%	$270.7717	$270.77	$270.75	$270.80
Purchase #6	$157.36	5.420%	$165.8889	$165.89	$165.90	$165.90
Purchase #7	$67.35	13.299%	$76.3069	$76.31	$76.30	$76.30
7 purchase totals =	$855.76		$939.6809	$939.69	$939.65	$939.70