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	$123.39	13.853%	$140.4832	$140.48	$140.50	$140.50
Purchase #2	$43.32	5.313%	$45.6216	$45.62	$45.60	$45.60
Purchase #3	$151.33	11.771%	$169.1431	$169.14	$169.15	$169.10
Purchase #4	$170.57	4.417%	$178.1041	$178.10	$178.10	$178.10
Purchase #5	$196.71	11.750%	$219.8234	$219.82	$219.80	$219.80
Purchase #6	$115.92	5.431%	$122.2156	$122.22	$122.20	$122.20
Purchase #7	$65.74	10.792%	$72.8347	$72.83	$72.85	$72.80
7 purchase totals =	$866.98		$948.2257	$948.21	$948.20	$948.10