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	$135.30	9.223%	$147.7787	$147.78	$147.80	$147.80
Purchase #2	$78.60	11.704%	$87.7993	$87.80	$87.80	$87.80
Purchase #3	$95.64	3.619%	$99.1012	$99.10	$99.10	$99.10
Purchase #4	$54.90	9.245%	$59.9755	$59.98	$60.00	$60.00
Purchase #5	$191.55	12.851%	$216.1661	$216.17	$216.15	$216.20
Purchase #6	$64.94	12.259%	$72.901	$72.90	$72.90	$72.90
Purchase #7	$44.59	4.765%	$46.7147	$46.71	$46.70	$46.70
7 purchase totals =	$665.52		$730.4365	$730.44	$730.45	$730.50