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	$53.40	13.441%	$60.5775	$60.58	$60.60	$60.60
Purchase #2	$55.84	6.248%	$59.3289	$59.33	$59.35	$59.30
Purchase #3	$98.51	6.684%	$105.0944	$105.09	$105.10	$105.10
Purchase #4	$164.87	10.290%	$181.8351	$181.84	$181.85	$181.80
Purchase #5	$8.54	3.354%	$8.8264	$8.83	$8.85	$8.80
Purchase #6	$218.95	11.406%	$243.9234	$243.92	$243.90	$243.90
Purchase #7	$82.39	7.769%	$88.7909	$88.79	$88.80	$88.80
7 purchase totals =	$682.50		$748.3766	$748.38	$748.45	$748.30