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	$11.30	12.362%	$12.6969	$12.70	$12.70	$12.70
Purchase #2	$102.29	6.677%	$109.1199	$109.12	$109.10	$109.10
Purchase #3	$166.28	5.181%	$174.895	$174.90	$174.90	$174.90
Purchase #4	$82.48	8.589%	$89.5642	$89.56	$89.55	$89.60
Purchase #5	$211.53	3.672%	$219.2974	$219.30	$219.30	$219.30
Purchase #6	$137.39	5.196%	$144.5288	$144.53	$144.55	$144.50
Purchase #7	$179.97	7.302%	$193.1114	$193.11	$193.10	$193.10
7 purchase totals =	$891.24		$943.2136	$943.22	$943.20	$943.20