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	$245.33	12.211%	$275.2872	$275.29	$275.30	$275.30
Purchase #2	$221.74	12.190%	$248.7701	$248.77	$248.75	$248.80
Purchase #3	$233.41	6.302%	$248.1195	$248.12	$248.10	$248.10
Purchase #4	$178.65	3.555%	$185.001	$185.00	$185.00	$185.00
Purchase #5	$39.37	8.771%	$42.8231	$42.82	$42.80	$42.80
Purchase #6	$125.61	4.533%	$131.3039	$131.30	$131.30	$131.30
Purchase #7	$135.39	13.401%	$153.5336	$153.53	$153.55	$153.50
7 purchase totals =	$1,179.50		$1,284.8384	$1,284.83	$1,284.80	$1,284.80