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	$66.30	8.761%	$72.1085	$72.11	$72.10	$72.10
Purchase #2	$37.55	3.223%	$38.7602	$38.76	$38.75	$38.80
Purchase #3	$11.65	3.172%	$12.0195	$12.02	$12.00	$12.00
Purchase #4	$91.58	7.656%	$98.5914	$98.59	$98.60	$98.60
Purchase #5	$112.97	6.144%	$119.9109	$119.91	$119.90	$119.90
Purchase #6	$210.27	13.527%	$238.7132	$238.71	$238.70	$238.70
Purchase #7	$246.70	11.398%	$274.8189	$274.82	$274.80	$274.80
7 purchase totals =	$777.02		$854.9226	$854.92	$854.85	$854.90