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	$244.61	12.200%	$274.4524	$274.45	$274.45	$274.50
Purchase #2	$55.60	8.370%	$60.2537	$60.25	$60.25	$60.30
Purchase #3	$103.93	4.611%	$108.7222	$108.72	$108.70	$108.70
Purchase #4	$169.32	9.363%	$185.1734	$185.17	$185.15	$185.20
Purchase #5	$115.30	11.154%	$128.1606	$128.16	$128.15	$128.20
Purchase #6	$22.73	8.443%	$24.6491	$24.65	$24.65	$24.60
Purchase #7	$250.76	7.351%	$269.1934	$269.19	$269.20	$269.20
7 purchase totals =	$962.25		$1,050.6048	$1,050.59	$1,050.55	$1,050.70