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	$83.62	7.761%	$90.1097	$90.11	$90.10	$90.10
Purchase #2	$64.57	8.629%	$70.1417	$70.14	$70.15	$70.10
Purchase #3	$69.36	3.490%	$71.7807	$71.78	$71.80	$71.80
Purchase #4	$211.71	12.189%	$237.5153	$237.52	$237.50	$237.50
Purchase #5	$249.28	10.269%	$274.8786	$274.88	$274.90	$274.90
Purchase #6	$130.67	3.254%	$134.922	$134.92	$134.90	$134.90
Purchase #7	$71.75	9.506%	$78.5706	$78.57	$78.55	$78.60
7 purchase totals =	$880.96		$957.9186	$957.92	$957.90	$957.90