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	$185.42	10.152%	$204.2438	$204.24	$204.25	$204.20
Purchase #2	$164.86	12.473%	$185.423	$185.42	$185.40	$185.40
Purchase #3	$240.66	4.230%	$250.8399	$250.84	$250.85	$250.80
Purchase #4	$57.42	7.145%	$61.5227	$61.52	$61.50	$61.50
Purchase #5	$73.98	11.583%	$82.5491	$82.55	$82.55	$82.50
Purchase #6	$154.67	9.824%	$169.8648	$169.86	$169.85	$169.90
Purchase #7	$151.66	7.277%	$162.6963	$162.70	$162.70	$162.70
7 purchase totals =	$1,028.67		$1,117.1396	$1,117.13	$1,117.10	$1,117.00