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	$41.68	4.370%	$43.5014	$43.50	$43.50	$43.50
Purchase #2	$208.83	12.720%	$235.3932	$235.39	$235.40	$235.40
Purchase #3	$49.72	10.382%	$54.8819	$54.88	$54.90	$54.90
Purchase #4	$109.31	10.656%	$120.9581	$120.96	$120.95	$121.00
Purchase #5	$135.71	8.434%	$147.1558	$147.16	$147.15	$147.20
Purchase #6	$152.88	8.265%	$165.5155	$165.52	$165.50	$165.50
Purchase #7	$98.63	4.591%	$103.1581	$103.16	$103.15	$103.20
7 purchase totals =	$796.76		$870.5640	$870.57	$870.55	$870.70