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	$158.79	7.791%	$171.1613	$171.16	$171.15	$171.20
Purchase #2	$176.53	6.386%	$187.8032	$187.80	$187.80	$187.80
Purchase #3	$248.77	3.774%	$258.1586	$258.16	$258.15	$258.20
Purchase #4	$85.67	5.313%	$90.2216	$90.22	$90.20	$90.20
Purchase #5	$18.32	13.794%	$20.8471	$20.85	$20.85	$20.80
Purchase #6	$62.81	3.308%	$64.8878	$64.89	$64.90	$64.90
Purchase #7	$192.41	5.731%	$203.437	$203.44	$203.45	$203.40
7 purchase totals =	$943.30		$996.5166	$996.52	$996.50	$996.50