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	$141.35	12.335%	$158.7855	$158.79	$158.80	$158.80
Purchase #2	$202.98	3.644%	$210.3766	$210.38	$210.40	$210.40
Purchase #3	$90.91	3.872%	$94.43	$94.43	$94.45	$94.40
Purchase #4	$201.61	5.531%	$212.761	$212.76	$212.75	$212.80
Purchase #5	$77.53	6.377%	$82.4741	$82.47	$82.45	$82.50
Purchase #6	$48.53	10.229%	$53.4941	$53.49	$53.50	$53.50
Purchase #7	$166.34	7.538%	$178.8787	$178.88	$178.90	$178.90
7 purchase totals =	$929.25		$991.2000	$991.20	$991.25	$991.30