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	$204.97	12.280%	$230.1403	$230.14	$230.15	$230.10
Purchase #2	$191.50	13.334%	$217.0346	$217.03	$217.05	$217.00
Purchase #3	$226.94	7.342%	$243.6019	$243.60	$243.60	$243.60
Purchase #4	$202.48	13.497%	$229.8087	$229.81	$229.80	$229.80
Purchase #5	$112.28	9.793%	$123.2756	$123.28	$123.30	$123.30
Purchase #6	$42.69	6.206%	$45.3393	$45.34	$45.35	$45.30
Purchase #7	$124.79	7.238%	$133.8223	$133.82	$133.80	$133.80
7 purchase totals =	$1,105.65		$1,223.0227	$1,223.02	$1,223.05	$1,222.90