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	$100.40	12.107%	$112.5554	$112.56	$112.55	$112.60
Purchase #2	$237.56	5.436%	$250.4738	$250.47	$250.45	$250.50
Purchase #3	$196.44	13.658%	$223.2698	$223.27	$223.25	$223.30
Purchase #4	$209.51	3.263%	$216.3463	$216.35	$216.35	$216.30
Purchase #5	$103.72	4.704%	$108.599	$108.60	$108.60	$108.60
Purchase #6	$30.74	6.674%	$32.7916	$32.79	$32.80	$32.80
Purchase #7	$71.93	6.569%	$76.6551	$76.66	$76.65	$76.70
7 purchase totals =	$950.30		$1,020.6910	$1,020.70	$1,020.65	$1,020.80