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	$114.88	6.117%	$121.9072	$121.91	$121.90	$121.90
Purchase #2	$40.86	12.844%	$46.1081	$46.11	$46.10	$46.10
Purchase #3	$146.32	3.640%	$151.646	$151.65	$151.65	$151.60
Purchase #4	$206.34	5.573%	$217.8393	$217.84	$217.85	$217.80
Purchase #5	$169.32	10.269%	$186.7075	$186.71	$186.70	$186.70
Purchase #6	$75.44	4.485%	$78.8235	$78.82	$78.80	$78.80
Purchase #7	$85.45	5.335%	$90.0088	$90.01	$90.00	$90.00
7 purchase totals =	$838.61		$893.0404	$893.05	$893.00	$892.90