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	$147.52	7.362%	$158.3804	$158.38	$158.40	$158.40
Purchase #2	$47.50	12.529%	$53.4513	$53.45	$53.45	$53.50
Purchase #3	$70.25	5.180%	$73.889	$73.89	$73.90	$73.90
Purchase #4	$81.54	13.329%	$92.4085	$92.41	$92.40	$92.40
Purchase #5	$70.80	12.649%	$79.7555	$79.76	$79.75	$79.80
Purchase #6	$174.68	3.366%	$180.5597	$180.56	$180.55	$180.60
Purchase #7	$21.92	11.347%	$24.4073	$24.41	$24.40	$24.40
7 purchase totals =	$614.21		$662.8517	$662.86	$662.85	$663.00