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	$67.97	4.829%	$71.2523	$71.25	$71.25	$71.30
Purchase #2	$184.70	13.488%	$209.6123	$209.61	$209.60	$209.60
Purchase #3	$238.58	13.411%	$270.576	$270.58	$270.60	$270.60
Purchase #4	$60.41	9.336%	$66.0499	$66.05	$66.05	$66.00
Purchase #5	$39.62	7.418%	$42.559	$42.56	$42.55	$42.60
Purchase #6	$226.56	8.536%	$245.8992	$245.90	$245.90	$245.90
Purchase #7	$247.29	13.180%	$279.8828	$279.88	$279.90	$279.90
7 purchase totals =	$1,065.13		$1,185.8315	$1,185.83	$1,185.85	$1,185.90