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	$139.31	6.576%	$148.471	$148.47	$148.45	$148.50
Purchase #2	$86.80	4.541%	$90.7416	$90.74	$90.75	$90.70
Purchase #3	$177.55	5.865%	$187.9633	$187.96	$187.95	$188.00
Purchase #4	$145.63	11.829%	$162.8566	$162.86	$162.85	$162.90
Purchase #5	$94.34	8.289%	$102.1598	$102.16	$102.15	$102.20
Purchase #6	$111.32	11.439%	$124.0539	$124.05	$124.05	$124.10
Purchase #7	$26.42	4.797%	$27.6874	$27.69	$27.70	$27.70
7 purchase totals =	$781.37		$843.9336	$843.93	$843.90	$844.10