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	$73.51	13.714%	$83.5912	$83.59	$83.60	$83.60
Purchase #2	$50.56	4.851%	$53.0127	$53.01	$53.00	$53.00
Purchase #3	$139.47	12.487%	$156.8856	$156.89	$156.90	$156.90
Purchase #4	$147.52	8.148%	$159.5399	$159.54	$159.55	$159.50
Purchase #5	$98.86	12.713%	$111.4281	$111.43	$111.45	$111.40
Purchase #6	$133.84	5.757%	$141.5452	$141.55	$141.55	$141.50
Purchase #7	$222.75	13.460%	$252.7322	$252.73	$252.75	$252.70
7 purchase totals =	$866.51		$958.7349	$958.74	$958.80	$958.60