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	$53.38	6.578%	$56.8913	$56.89	$56.90	$56.90
Purchase #2	$67.44	7.191%	$72.2896	$72.29	$72.30	$72.30
Purchase #3	$103.62	3.850%	$107.6094	$107.61	$107.60	$107.60
Purchase #4	$243.76	13.531%	$276.7432	$276.74	$276.75	$276.70
Purchase #5	$62.87	3.792%	$65.254	$65.25	$65.25	$65.30
Purchase #6	$50.76	3.179%	$52.3737	$52.37	$52.35	$52.40
Purchase #7	$45.90	3.642%	$47.5717	$47.57	$47.55	$47.60
7 purchase totals =	$627.73		$678.7329	$678.72	$678.70	$678.80