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	$88.96	13.331%	$100.8193	$100.82	$100.80	$100.80
Purchase #2	$190.99	12.770%	$215.3794	$215.38	$215.40	$215.40
Purchase #3	$163.34	7.708%	$175.9302	$175.93	$175.95	$175.90
Purchase #4	$99.59	9.160%	$108.7124	$108.71	$108.70	$108.70
Purchase #5	$246.67	12.308%	$277.0301	$277.03	$277.05	$277.00
Purchase #6	$148.69	7.156%	$159.3303	$159.33	$159.35	$159.30
Purchase #7	$78.38	13.600%	$89.0397	$89.04	$89.05	$89.00
7 purchase totals =	$1,016.62		$1,126.2414	$1,126.24	$1,126.30	$1,126.10