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	$188.91	4.228%	$196.8971	$196.90	$196.90	$196.90
Purchase #2	$34.83	11.606%	$38.8724	$38.87	$38.85	$38.90
Purchase #3	$210.36	9.298%	$229.9193	$229.92	$229.90	$229.90
Purchase #4	$231.64	4.740%	$242.6197	$242.62	$242.60	$242.60
Purchase #5	$67.25	3.440%	$69.5634	$69.56	$69.55	$69.60
Purchase #6	$22.42	13.524%	$25.4521	$25.45	$25.45	$25.50
Purchase #7	$47.59	3.321%	$49.1705	$49.17	$49.15	$49.20
7 purchase totals =	$803.00		$852.4945	$852.49	$852.40	$852.60