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	$81.99	6.391%	$87.23	$87.23	$87.25	$87.20
Purchase #2	$36.56	6.221%	$38.8344	$38.83	$38.85	$38.80
Purchase #3	$119.87	6.343%	$127.4734	$127.47	$127.45	$127.50
Purchase #4	$124.39	12.130%	$139.4785	$139.48	$139.50	$139.50
Purchase #5	$101.83	13.424%	$115.4997	$115.50	$115.50	$115.50
Purchase #6	$151.50	5.560%	$159.9234	$159.92	$159.90	$159.90
Purchase #7	$85.31	8.764%	$92.7866	$92.79	$92.80	$92.80
7 purchase totals =	$701.45		$761.2260	$761.22	$761.25	$761.20