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	$236.90	13.858%	$269.7296	$269.73	$269.75	$269.70
Purchase #2	$10.43	12.665%	$11.751	$11.75	$11.75	$11.80
Purchase #3	$85.33	6.755%	$91.094	$91.09	$91.10	$91.10
Purchase #4	$143.25	8.401%	$155.2844	$155.28	$155.30	$155.30
Purchase #5	$245.45	13.459%	$278.4851	$278.49	$278.50	$278.50
Purchase #6	$249.79	12.451%	$280.8914	$280.89	$280.90	$280.90
Purchase #7	$30.90	7.441%	$33.1993	$33.20	$33.20	$33.20
7 purchase totals =	$1,002.05		$1,120.4348	$1,120.43	$1,120.50	$1,120.50