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	$46.87	12.864%	$52.8994	$52.90	$52.90	$52.90
Purchase #2	$62.58	7.714%	$67.4074	$67.41	$67.40	$67.40
Purchase #3	$27.82	10.539%	$30.7519	$30.75	$30.75	$30.80
Purchase #4	$65.88	7.764%	$70.9949	$70.99	$71.00	$71.00
Purchase #5	$224.51	11.577%	$250.5015	$250.50	$250.50	$250.50
Purchase #6	$37.53	13.843%	$42.7253	$42.73	$42.75	$42.70
Purchase #7	$139.94	9.757%	$153.5939	$153.59	$153.60	$153.60
7 purchase totals =	$605.13		$668.8743	$668.87	$668.90	$668.90