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	$90.70	7.414%	$97.4245	$97.42	$97.40	$97.40
Purchase #2	$160.74	12.552%	$180.9161	$180.92	$180.90	$180.90
Purchase #3	$215.31	10.663%	$238.2685	$238.27	$238.25	$238.30
Purchase #4	$201.47	11.665%	$224.9715	$224.97	$224.95	$225.00
Purchase #5	$195.55	13.688%	$222.3169	$222.32	$222.30	$222.30
Purchase #6	$16.70	12.513%	$18.7897	$18.79	$18.80	$18.80
Purchase #7	$91.69	8.791%	$99.7505	$99.75	$99.75	$99.80
7 purchase totals =	$972.16		$1,082.4377	$1,082.44	$1,082.35	$1,082.50