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	$183.29	4.158%	$190.9112	$190.91	$190.90	$190.90
Purchase #2	$63.97	10.536%	$70.7099	$70.71	$70.70	$70.70
Purchase #3	$60.26	8.736%	$65.5243	$65.52	$65.50	$65.50
Purchase #4	$233.81	13.599%	$265.6058	$265.61	$265.60	$265.60
Purchase #5	$95.34	3.428%	$98.6083	$98.61	$98.60	$98.60
Purchase #6	$159.58	4.847%	$167.3148	$167.31	$167.30	$167.30
Purchase #7	$15.31	4.121%	$15.9409	$15.94	$15.95	$15.90
7 purchase totals =	$811.56		$874.6152	$874.61	$874.55	$874.50