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	$177.96	6.432%	$189.4064	$189.41	$189.40	$189.40
Purchase #2	$65.51	5.254%	$68.9519	$68.95	$68.95	$69.00
Purchase #3	$119.66	6.325%	$127.2285	$127.23	$127.25	$127.20
Purchase #4	$60.40	12.219%	$67.7803	$67.78	$67.80	$67.80
Purchase #5	$32.39	8.819%	$35.2465	$35.25	$35.25	$35.20
Purchase #6	$63.59	11.501%	$70.9035	$70.90	$70.90	$70.90
Purchase #7	$67.85	4.826%	$71.1244	$71.12	$71.10	$71.10
7 purchase totals =	$587.36		$630.6415	$630.64	$630.65	$630.60