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	$79.53	13.426%	$90.2077	$90.21	$90.20	$90.20
Purchase #2	$67.56	9.709%	$74.1194	$74.12	$74.10	$74.10
Purchase #3	$98.44	7.430%	$105.7541	$105.75	$105.75	$105.80
Purchase #4	$211.47	11.178%	$235.1081	$235.11	$235.10	$235.10
Purchase #5	$93.88	5.695%	$99.2265	$99.23	$99.25	$99.20
Purchase #6	$34.44	8.119%	$37.2362	$37.24	$37.25	$37.20
Purchase #7	$100.59	11.750%	$112.4093	$112.41	$112.40	$112.40
7 purchase totals =	$685.91		$754.0613	$754.07	$754.05	$754.00