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	$188.59	8.321%	$204.2826	$204.28	$204.30	$204.30
Purchase #2	$200.89	4.837%	$210.607	$210.61	$210.60	$210.60
Purchase #3	$35.70	12.736%	$40.2468	$40.25	$40.25	$40.20
Purchase #4	$208.93	5.224%	$219.8445	$219.84	$219.85	$219.80
Purchase #5	$143.59	5.658%	$151.7143	$151.71	$151.70	$151.70
Purchase #6	$244.98	9.754%	$268.8753	$268.88	$268.90	$268.90
Purchase #7	$40.55	7.149%	$43.4489	$43.45	$43.45	$43.40
7 purchase totals =	$1,063.23		$1,139.0194	$1,139.02	$1,139.05	$1,138.90