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	$216.71	12.711%	$244.256	$244.26	$244.25	$244.30
Purchase #2	$45.54	10.116%	$50.1468	$50.15	$50.15	$50.10
Purchase #3	$46.84	7.228%	$50.2256	$50.23	$50.25	$50.20
Purchase #4	$81.74	9.631%	$89.6124	$89.61	$89.60	$89.60
Purchase #5	$229.83	6.609%	$245.0195	$245.02	$245.00	$245.00
Purchase #6	$36.90	8.851%	$40.166	$40.17	$40.15	$40.20
Purchase #7	$162.77	5.192%	$171.221	$171.22	$171.20	$171.20
7 purchase totals =	$820.33		$890.6473	$890.66	$890.60	$890.60