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	$62.51	12.636%	$70.4088	$70.41	$70.40	$70.40
Purchase #2	$105.30	5.728%	$111.3316	$111.33	$111.35	$111.30
Purchase #3	$42.46	6.663%	$45.2891	$45.29	$45.30	$45.30
Purchase #4	$187.76	3.794%	$194.8836	$194.88	$194.90	$194.90
Purchase #5	$127.77	6.469%	$136.0354	$136.04	$136.05	$136.00
Purchase #6	$78.46	12.857%	$88.5476	$88.55	$88.55	$88.50
Purchase #7	$82.67	13.430%	$93.7726	$93.77	$93.75	$93.80
7 purchase totals =	$686.93		$740.2687	$740.27	$740.30	$740.20