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	$11.70	7.374%	$12.5628	$12.56	$12.55	$12.60
Purchase #2	$155.32	3.578%	$160.8773	$160.88	$160.90	$160.90
Purchase #3	$113.62	5.734%	$120.135	$120.14	$120.15	$120.10
Purchase #4	$50.29	13.127%	$56.8916	$56.89	$56.90	$56.90
Purchase #5	$66.27	7.604%	$71.3092	$71.31	$71.30	$71.30
Purchase #6	$78.95	12.550%	$88.8582	$88.86	$88.85	$88.90
Purchase #7	$142.67	5.670%	$150.7594	$150.76	$150.75	$150.80
7 purchase totals =	$618.82		$661.3935	$661.40	$661.40	$661.50