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	$147.66	11.812%	$165.1016	$165.10	$165.10	$165.10
Purchase #2	$180.64	6.246%	$191.9228	$191.92	$191.90	$191.90
Purchase #3	$183.27	13.799%	$208.5594	$208.56	$208.55	$208.60
Purchase #4	$73.67	6.152%	$78.2022	$78.20	$78.20	$78.20
Purchase #5	$165.98	13.702%	$188.7226	$188.72	$188.70	$188.70
Purchase #6	$73.25	6.743%	$78.1892	$78.19	$78.20	$78.20
Purchase #7	$39.54	4.474%	$41.309	$41.31	$41.30	$41.30
7 purchase totals =	$864.01		$952.0068	$952.00	$951.95	$952.00