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	$115.81	7.778%	$124.8177	$124.82	$124.80	$124.80
Purchase #2	$56.91	4.410%	$59.4197	$59.42	$59.40	$59.40
Purchase #3	$170.45	11.197%	$189.5353	$189.54	$189.55	$189.50
Purchase #4	$94.91	6.523%	$101.101	$101.10	$101.10	$101.10
Purchase #5	$62.48	12.431%	$70.2469	$70.25	$70.25	$70.20
Purchase #6	$61.97	11.490%	$69.0904	$69.09	$69.10	$69.10
Purchase #7	$91.47	8.359%	$99.116	$99.12	$99.10	$99.10
7 purchase totals =	$654.00		$713.3270	$713.34	$713.30	$713.20