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	$158.51	4.698%	$165.9568	$165.96	$165.95	$166.00
Purchase #2	$91.40	5.718%	$96.6263	$96.63	$96.65	$96.60
Purchase #3	$172.90	10.228%	$190.5842	$190.58	$190.60	$190.60
Purchase #4	$173.97	11.740%	$194.3941	$194.39	$194.40	$194.40
Purchase #5	$216.92	6.482%	$230.9808	$230.98	$231.00	$231.00
Purchase #6	$41.61	10.356%	$45.9191	$45.92	$45.90	$45.90
Purchase #7	$30.34	3.515%	$31.4065	$31.41	$31.40	$31.40
7 purchase totals =	$885.65		$955.8678	$955.87	$955.90	$955.90