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	$172.70	3.684%	$179.0623	$179.06	$179.05	$179.10
Purchase #2	$119.78	6.279%	$127.301	$127.30	$127.30	$127.30
Purchase #3	$47.47	12.547%	$53.4261	$53.43	$53.45	$53.40
Purchase #4	$106.53	12.752%	$120.1147	$120.11	$120.10	$120.10
Purchase #5	$113.32	13.565%	$128.6919	$128.69	$128.70	$128.70
Purchase #6	$47.29	13.370%	$53.6127	$53.61	$53.60	$53.60
Purchase #7	$218.63	11.300%	$243.3352	$243.34	$243.35	$243.30
7 purchase totals =	$825.72		$905.5439	$905.54	$905.55	$905.50