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	$200.53	7.806%	$216.1834	$216.18	$216.20	$216.20
Purchase #2	$94.93	10.715%	$105.1017	$105.10	$105.10	$105.10
Purchase #3	$200.56	8.672%	$217.9526	$217.95	$217.95	$218.00
Purchase #4	$79.27	13.582%	$90.0365	$90.04	$90.05	$90.00
Purchase #5	$64.42	12.222%	$72.2934	$72.29	$72.30	$72.30
Purchase #6	$229.73	9.124%	$250.6906	$250.69	$250.70	$250.70
Purchase #7	$50.74	12.630%	$57.1485	$57.15	$57.15	$57.10
7 purchase totals =	$920.18		$1,009.4067	$1,009.40	$1,009.45	$1,009.40