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	$32.95	9.533%	$36.0911	$36.09	$36.10	$36.10
Purchase #2	$111.72	10.579%	$123.5389	$123.54	$123.55	$123.50
Purchase #3	$95.92	10.574%	$106.0626	$106.06	$106.05	$106.10
Purchase #4	$27.89	3.207%	$28.7844	$28.78	$28.80	$28.80
Purchase #5	$195.72	10.668%	$216.5994	$216.60	$216.60	$216.60
Purchase #6	$90.53	10.355%	$99.9044	$99.90	$99.90	$99.90
Purchase #7	$192.97	13.234%	$218.5076	$218.51	$218.50	$218.50
7 purchase totals =	$747.70		$829.4884	$829.48	$829.50	$829.50