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	$29.86	13.343%	$33.8442	$33.84	$33.85	$33.80
Purchase #2	$155.34	6.546%	$165.5086	$165.51	$165.50	$165.50
Purchase #3	$82.30	13.520%	$93.427	$93.43	$93.45	$93.40
Purchase #4	$107.55	9.218%	$117.464	$117.46	$117.45	$117.50
Purchase #5	$38.43	3.494%	$39.7727	$39.77	$39.75	$39.80
Purchase #6	$145.72	3.819%	$151.285	$151.29	$151.30	$151.30
Purchase #7	$35.89	12.382%	$40.3339	$40.33	$40.35	$40.30
7 purchase totals =	$595.09		$641.6354	$641.63	$641.65	$641.60