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	$13.74	8.382%	$14.8917	$14.89	$14.90	$14.90
Purchase #2	$68.79	11.678%	$76.8233	$76.82	$76.80	$76.80
Purchase #3	$173.53	8.690%	$188.6098	$188.61	$188.60	$188.60
Purchase #4	$248.27	7.421%	$266.6941	$266.69	$266.70	$266.70
Purchase #5	$247.56	9.817%	$271.863	$271.86	$271.85	$271.90
Purchase #6	$212.99	5.460%	$224.6193	$224.62	$224.60	$224.60
Purchase #7	$50.71	12.853%	$57.2278	$57.23	$57.25	$57.20
7 purchase totals =	$1,015.59		$1,100.7290	$1,100.72	$1,100.70	$1,100.70