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	$18.42	6.366%	$19.5926	$19.59	$19.60	$19.60
Purchase #2	$57.44	8.528%	$62.3385	$62.34	$62.35	$62.30
Purchase #3	$245.47	11.329%	$273.2793	$273.28	$273.30	$273.30
Purchase #4	$61.92	3.613%	$64.1572	$64.16	$64.15	$64.20
Purchase #5	$32.41	11.290%	$36.0691	$36.07	$36.05	$36.10
Purchase #6	$85.91	4.609%	$89.8696	$89.87	$89.85	$89.90
Purchase #7	$6.33	9.231%	$6.9143	$6.91	$6.90	$6.90
7 purchase totals =	$507.90		$552.2206	$552.22	$552.20	$552.30