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	$233.29	12.128%	$261.5834	$261.58	$261.60	$261.60
Purchase #2	$93.53	3.645%	$96.9392	$96.94	$96.95	$96.90
Purchase #3	$166.55	11.594%	$185.8598	$185.86	$185.85	$185.90
Purchase #4	$159.65	13.650%	$181.4422	$181.44	$181.45	$181.40
Purchase #5	$143.70	13.216%	$162.6914	$162.69	$162.70	$162.70
Purchase #6	$168.83	11.637%	$188.4767	$188.48	$188.50	$188.50
Purchase #7	$90.38	10.619%	$99.9775	$99.98	$100.00	$100.00
7 purchase totals =	$1,055.93		$1,176.9702	$1,176.97	$1,177.05	$1,177.00