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	$198.68	5.281%	$209.1723	$209.17	$209.15	$209.20
Purchase #2	$100.72	9.288%	$110.0749	$110.07	$110.05	$110.10
Purchase #3	$203.92	10.773%	$225.8883	$225.89	$225.90	$225.90
Purchase #4	$156.77	11.837%	$175.3269	$175.33	$175.35	$175.30
Purchase #5	$182.62	7.417%	$196.1649	$196.16	$196.15	$196.20
Purchase #6	$141.31	8.568%	$153.4174	$153.42	$153.40	$153.40
Purchase #7	$245.89	11.765%	$274.819	$274.82	$274.80	$274.80
7 purchase totals =	$1,229.91		$1,344.8637	$1,344.86	$1,344.80	$1,344.90