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	$139.82	12.130%	$156.7802	$156.78	$156.80	$156.80
Purchase #2	$37.69	9.392%	$41.2298	$41.23	$41.25	$41.20
Purchase #3	$83.53	3.556%	$86.5003	$86.50	$86.50	$86.50
Purchase #4	$53.43	4.628%	$55.9027	$55.90	$55.90	$55.90
Purchase #5	$234.69	5.865%	$248.4546	$248.45	$248.45	$248.50
Purchase #6	$29.84	13.325%	$33.8162	$33.82	$33.80	$33.80
Purchase #7	$127.97	7.634%	$137.7392	$137.74	$137.75	$137.70
7 purchase totals =	$706.97		$760.4230	$760.42	$760.45	$760.40