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	$19.72	13.556%	$22.3932	$22.39	$22.40	$22.40
Purchase #2	$133.45	11.540%	$148.8501	$148.85	$148.85	$148.90
Purchase #3	$240.41	13.667%	$273.2668	$273.27	$273.25	$273.30
Purchase #4	$19.73	3.441%	$20.4089	$20.41	$20.40	$20.40
Purchase #5	$79.97	4.254%	$83.3719	$83.37	$83.35	$83.40
Purchase #6	$215.28	13.870%	$245.1393	$245.14	$245.15	$245.10
Purchase #7	$99.98	5.669%	$105.6479	$105.65	$105.65	$105.60
7 purchase totals =	$808.54		$899.0781	$899.08	$899.05	$899.10