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	$86.45	6.294%	$91.8912	$91.89	$91.90	$91.90
Purchase #2	$173.82	9.197%	$189.8062	$189.81	$189.80	$189.80
Purchase #3	$214.95	3.869%	$223.2664	$223.27	$223.25	$223.30
Purchase #4	$218.90	10.673%	$242.2632	$242.26	$242.25	$242.30
Purchase #5	$89.40	4.589%	$93.5026	$93.50	$93.50	$93.50
Purchase #6	$243.37	13.783%	$276.9137	$276.91	$276.90	$276.90
Purchase #7	$171.34	11.252%	$190.6192	$190.62	$190.60	$190.60
7 purchase totals =	$1,198.23		$1,308.2625	$1,308.26	$1,308.20	$1,308.30