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	$91.90	8.789%	$99.9771	$99.98	$100.00	$100.00
Purchase #2	$142.46	7.308%	$152.871	$152.87	$152.85	$152.90
Purchase #3	$165.91	3.771%	$172.1665	$172.17	$172.15	$172.20
Purchase #4	$217.25	3.528%	$224.9146	$224.91	$224.90	$224.90
Purchase #5	$65.54	12.572%	$73.7797	$73.78	$73.80	$73.80
Purchase #6	$130.79	8.769%	$142.259	$142.26	$142.25	$142.30
Purchase #7	$125.59	9.556%	$137.5914	$137.59	$137.60	$137.60
7 purchase totals =	$939.44		$1,003.5593	$1,003.56	$1,003.55	$1,003.70