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	$33.89	11.363%	$37.7409	$37.74	$37.75	$37.70
Purchase #2	$104.25	5.647%	$110.137	$110.14	$110.15	$110.10
Purchase #3	$108.64	13.741%	$123.5682	$123.57	$123.55	$123.60
Purchase #4	$218.83	11.520%	$244.0392	$244.04	$244.05	$244.00
Purchase #5	$208.85	9.815%	$229.3486	$229.35	$229.35	$229.30
Purchase #6	$141.26	7.531%	$151.8983	$151.90	$151.90	$151.90
Purchase #7	$131.34	8.454%	$142.4435	$142.44	$142.45	$142.40
7 purchase totals =	$947.06		$1,039.1757	$1,039.18	$1,039.20	$1,039.00