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	$173.57	7.806%	$187.1189	$187.12	$187.10	$187.10
Purchase #2	$170.34	10.238%	$187.7794	$187.78	$187.80	$187.80
Purchase #3	$193.36	13.258%	$218.9957	$219.00	$219.00	$219.00
Purchase #4	$117.85	11.612%	$131.5347	$131.53	$131.55	$131.50
Purchase #5	$54.29	6.332%	$57.7276	$57.73	$57.75	$57.70
Purchase #6	$209.48	10.567%	$231.6158	$231.62	$231.60	$231.60
Purchase #7	$101.34	7.110%	$108.5453	$108.55	$108.55	$108.50
7 purchase totals =	$1,020.23		$1,123.3174	$1,123.33	$1,123.35	$1,123.20