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	$69.35	5.443%	$73.1247	$73.12	$73.10	$73.10
Purchase #2	$59.59	9.593%	$65.3065	$65.31	$65.30	$65.30
Purchase #3	$55.50	7.705%	$59.7763	$59.78	$59.80	$59.80
Purchase #4	$93.59	7.536%	$100.6429	$100.64	$100.65	$100.60
Purchase #5	$224.30	13.264%	$254.0512	$254.05	$254.05	$254.10
Purchase #6	$98.42	7.693%	$105.9915	$105.99	$106.00	$106.00
Purchase #7	$193.50	13.772%	$220.1488	$220.15	$220.15	$220.10
7 purchase totals =	$794.25		$879.0419	$879.04	$879.05	$879.00