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	$209.81	9.227%	$229.1692	$229.17	$229.15	$229.20
Purchase #2	$116.54	12.470%	$131.0725	$131.07	$131.05	$131.10
Purchase #3	$200.26	13.680%	$227.6556	$227.66	$227.65	$227.70
Purchase #4	$168.83	8.589%	$183.3308	$183.33	$183.35	$183.30
Purchase #5	$158.70	6.736%	$169.39	$169.39	$169.40	$169.40
Purchase #6	$82.53	7.646%	$88.8402	$88.84	$88.85	$88.80
Purchase #7	$81.62	10.138%	$89.8946	$89.89	$89.90	$89.90
7 purchase totals =	$1,018.29		$1,119.3529	$1,119.35	$1,119.35	$1,119.40