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	$75.82	3.805%	$78.705	$78.71	$78.70	$78.70
Purchase #2	$240.80	10.528%	$266.1514	$266.15	$266.15	$266.20
Purchase #3	$205.90	5.351%	$216.9177	$216.92	$216.90	$216.90
Purchase #4	$175.27	5.609%	$185.1009	$185.10	$185.10	$185.10
Purchase #5	$70.40	3.369%	$72.7718	$72.77	$72.75	$72.80
Purchase #6	$180.58	12.547%	$203.2374	$203.24	$203.25	$203.20
Purchase #7	$43.57	7.373%	$46.7824	$46.78	$46.80	$46.80
7 purchase totals =	$992.34		$1,069.6666	$1,069.67	$1,069.65	$1,069.70