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	$94.92	11.848%	$106.1661	$106.17	$106.15	$106.20
Purchase #2	$246.87	11.531%	$275.3366	$275.34	$275.35	$275.30
Purchase #3	$135.69	9.740%	$148.9062	$148.91	$148.90	$148.90
Purchase #4	$128.93	5.767%	$136.3654	$136.37	$136.35	$136.40
Purchase #5	$162.37	11.571%	$181.1578	$181.16	$181.15	$181.20
Purchase #6	$82.74	9.659%	$90.7319	$90.73	$90.75	$90.70
Purchase #7	$60.32	10.863%	$66.8726	$66.87	$66.85	$66.90
7 purchase totals =	$911.84		$1,005.5366	$1,005.55	$1,005.50	$1,005.60