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	$105.98	13.738%	$120.5395	$120.54	$120.55	$120.50
Purchase #2	$189.32	12.433%	$212.8582	$212.86	$212.85	$212.90
Purchase #3	$197.39	12.576%	$222.2138	$222.21	$222.20	$222.20
Purchase #4	$215.61	4.309%	$224.9006	$224.90	$224.90	$224.90
Purchase #5	$159.53	12.569%	$179.5813	$179.58	$179.60	$179.60
Purchase #6	$66.43	5.794%	$70.279	$70.28	$70.30	$70.30
Purchase #7	$213.30	6.793%	$227.7895	$227.79	$227.80	$227.80
7 purchase totals =	$1,147.56		$1,258.1619	$1,258.16	$1,258.20	$1,258.20