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	$89.65	11.661%	$100.1041	$100.10	$100.10	$100.10
Purchase #2	$121.26	11.258%	$134.9115	$134.91	$134.90	$134.90
Purchase #3	$157.33	11.759%	$175.8304	$175.83	$175.85	$175.80
Purchase #4	$113.89	8.591%	$123.6743	$123.67	$123.65	$123.70
Purchase #5	$18.62	11.653%	$20.7898	$20.79	$20.80	$20.80
Purchase #6	$250.50	10.872%	$277.7344	$277.73	$277.75	$277.70
Purchase #7	$151.38	12.866%	$170.8566	$170.86	$170.85	$170.90
7 purchase totals =	$902.63		$1,003.9011	$1,003.89	$1,003.90	$1,003.90