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	$179.35	3.289%	$185.2488	$185.25	$185.25	$185.20
Purchase #2	$81.28	11.401%	$90.5467	$90.55	$90.55	$90.50
Purchase #3	$216.89	4.639%	$226.9515	$226.95	$226.95	$227.00
Purchase #4	$105.81	3.502%	$109.5155	$109.52	$109.50	$109.50
Purchase #5	$90.83	12.130%	$101.8477	$101.85	$101.85	$101.80
Purchase #6	$209.85	11.171%	$233.2923	$233.29	$233.30	$233.30
Purchase #7	$143.77	9.278%	$157.109	$157.11	$157.10	$157.10
7 purchase totals =	$1,027.78		$1,104.5115	$1,104.52	$1,104.50	$1,104.40