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	$43.72	10.457%	$48.2918	$48.29	$48.30	$48.30
Purchase #2	$19.86	10.434%	$21.9322	$21.93	$21.95	$21.90
Purchase #3	$144.39	6.815%	$154.2302	$154.23	$154.25	$154.20
Purchase #4	$85.46	3.686%	$88.6101	$88.61	$88.60	$88.60
Purchase #5	$135.65	3.281%	$140.1007	$140.10	$140.10	$140.10
Purchase #6	$218.89	6.496%	$233.1091	$233.11	$233.10	$233.10
Purchase #7	$112.93	12.765%	$127.3455	$127.35	$127.35	$127.30
7 purchase totals =	$760.90		$813.6196	$813.62	$813.65	$813.50