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	$135.34	4.260%	$141.1055	$141.11	$141.10	$141.10
Purchase #2	$62.34	8.805%	$67.829	$67.83	$67.85	$67.80
Purchase #3	$104.60	13.629%	$118.8559	$118.86	$118.85	$118.90
Purchase #4	$69.31	5.726%	$73.2787	$73.28	$73.30	$73.30
Purchase #5	$11.44	4.401%	$11.9435	$11.94	$11.95	$11.90
Purchase #6	$181.66	3.578%	$188.1598	$188.16	$188.15	$188.20
Purchase #7	$79.69	12.679%	$89.7939	$89.79	$89.80	$89.80
7 purchase totals =	$644.38		$690.9663	$690.97	$691.00	$691.00