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	$113.52	5.772%	$120.0724	$120.07	$120.05	$120.10
Purchase #2	$64.35	11.506%	$71.7541	$71.75	$71.75	$71.80
Purchase #3	$118.33	11.460%	$131.8906	$131.89	$131.90	$131.90
Purchase #4	$114.67	4.317%	$119.6203	$119.62	$119.60	$119.60
Purchase #5	$239.68	6.756%	$255.8728	$255.87	$255.85	$255.90
Purchase #6	$66.74	6.191%	$70.8719	$70.87	$70.85	$70.90
Purchase #7	$249.64	4.277%	$260.3171	$260.32	$260.30	$260.30
7 purchase totals =	$966.93		$1,030.3992	$1,030.39	$1,030.30	$1,030.50