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	$152.30	5.574%	$160.7892	$160.79	$160.80	$160.80
Purchase #2	$235.29	9.170%	$256.8661	$256.87	$256.85	$256.90
Purchase #3	$135.30	11.220%	$150.4807	$150.48	$150.50	$150.50
Purchase #4	$133.48	9.789%	$146.5464	$146.55	$146.55	$146.50
Purchase #5	$97.50	9.723%	$106.9799	$106.98	$107.00	$107.00
Purchase #6	$135.33	12.231%	$151.8822	$151.88	$151.90	$151.90
Purchase #7	$92.86	4.364%	$96.9124	$96.91	$96.90	$96.90
7 purchase totals =	$982.06		$1,070.4569	$1,070.46	$1,070.50	$1,070.50