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	$62.72	11.632%	$70.0156	$70.02	$70.00	$70.00
Purchase #2	$196.29	6.861%	$209.7575	$209.76	$209.75	$209.80
Purchase #3	$41.97	4.492%	$43.8553	$43.86	$43.85	$43.90
Purchase #4	$186.54	7.309%	$200.1742	$200.17	$200.15	$200.20
Purchase #5	$116.34	12.839%	$131.2769	$131.28	$131.30	$131.30
Purchase #6	$100.93	9.154%	$110.1691	$110.17	$110.15	$110.20
Purchase #7	$35.72	10.377%	$39.4267	$39.43	$39.45	$39.40
7 purchase totals =	$740.51		$804.6753	$804.69	$804.65	$804.80