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	$98.67	12.799%	$111.2988	$111.30	$111.30	$111.30
Purchase #2	$71.42	9.688%	$78.3392	$78.34	$78.35	$78.30
Purchase #3	$171.42	7.815%	$184.8165	$184.82	$184.80	$184.80
Purchase #4	$130.44	6.729%	$139.2173	$139.22	$139.20	$139.20
Purchase #5	$129.56	6.648%	$138.1731	$138.17	$138.15	$138.20
Purchase #6	$70.96	5.788%	$75.0672	$75.07	$75.05	$75.10
Purchase #7	$205.87	5.172%	$216.5176	$216.52	$216.50	$216.50
7 purchase totals =	$878.34		$943.4297	$943.44	$943.35	$943.40