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	$128.59	3.306%	$132.8412	$132.84	$132.85	$132.80
Purchase #2	$82.36	9.223%	$89.9561	$89.96	$89.95	$90.00
Purchase #3	$56.87	9.689%	$62.3801	$62.38	$62.40	$62.40
Purchase #4	$100.98	3.488%	$104.5022	$104.50	$104.50	$104.50
Purchase #5	$73.79	11.766%	$82.4721	$82.47	$82.45	$82.50
Purchase #6	$235.89	13.231%	$267.1006	$267.10	$267.10	$267.10
Purchase #7	$119.89	3.852%	$124.5082	$124.51	$124.50	$124.50
7 purchase totals =	$798.37		$863.7605	$863.76	$863.75	$863.80