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	$234.69	8.151%	$253.8196	$253.82	$253.80	$253.80
Purchase #2	$32.78	6.302%	$34.8458	$34.85	$34.85	$34.80
Purchase #3	$69.81	3.631%	$72.3448	$72.34	$72.35	$72.30
Purchase #4	$139.31	11.524%	$155.3641	$155.36	$155.35	$155.40
Purchase #5	$14.82	4.216%	$15.4448	$15.44	$15.45	$15.40
Purchase #6	$159.88	3.272%	$165.1113	$165.11	$165.10	$165.10
Purchase #7	$73.49	11.725%	$82.1067	$82.11	$82.10	$82.10
7 purchase totals =	$724.78		$779.0371	$779.03	$779.00	$778.90