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	$245.66	4.209%	$255.9998	$256.00	$256.00	$256.00
Purchase #2	$55.62	11.306%	$61.9084	$61.91	$61.90	$61.90
Purchase #3	$193.43	11.621%	$215.9085	$215.91	$215.90	$215.90
Purchase #4	$130.61	6.838%	$139.5411	$139.54	$139.55	$139.50
Purchase #5	$17.70	13.596%	$20.1065	$20.11	$20.10	$20.10
Purchase #6	$243.67	13.467%	$276.485	$276.49	$276.50	$276.50
Purchase #7	$159.88	9.326%	$174.7904	$174.79	$174.80	$174.80
7 purchase totals =	$1,046.57		$1,144.7397	$1,144.75	$1,144.75	$1,144.70