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	$159.91	6.797%	$170.7791	$170.78	$170.80	$170.80
Purchase #2	$250.98	10.468%	$277.2526	$277.25	$277.25	$277.30
Purchase #3	$97.69	12.518%	$109.9188	$109.92	$109.90	$109.90
Purchase #4	$219.83	4.453%	$229.619	$229.62	$229.60	$229.60
Purchase #5	$46.36	4.143%	$48.2807	$48.28	$48.30	$48.30
Purchase #6	$74.41	9.323%	$81.3472	$81.35	$81.35	$81.30
Purchase #7	$96.57	3.129%	$99.5917	$99.59	$99.60	$99.60
7 purchase totals =	$945.75		$1,016.7891	$1,016.79	$1,016.80	$1,016.80