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	$242.53	5.480%	$255.8206	$255.82	$255.80	$255.80
Purchase #2	$193.73	3.417%	$200.3498	$200.35	$200.35	$200.30
Purchase #3	$62.86	7.552%	$67.6072	$67.61	$67.60	$67.60
Purchase #4	$63.83	9.839%	$70.1102	$70.11	$70.10	$70.10
Purchase #5	$18.32	10.727%	$20.2852	$20.29	$20.30	$20.30
Purchase #6	$205.99	6.155%	$218.6687	$218.67	$218.65	$218.70
Purchase #7	$44.53	12.748%	$50.2067	$50.21	$50.20	$50.20
7 purchase totals =	$831.79		$883.0484	$883.06	$883.00	$883.00