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	$84.49	4.703%	$88.4636	$88.46	$88.45	$88.50
Purchase #2	$32.88	10.753%	$36.4156	$36.42	$36.40	$36.40
Purchase #3	$100.70	12.687%	$113.4758	$113.48	$113.50	$113.50
Purchase #4	$204.88	6.589%	$218.3795	$218.38	$218.40	$218.40
Purchase #5	$156.91	10.853%	$173.9394	$173.94	$173.95	$173.90
Purchase #6	$85.83	4.331%	$89.5473	$89.55	$89.55	$89.50
Purchase #7	$71.32	9.781%	$78.2958	$78.30	$78.30	$78.30
7 purchase totals =	$737.01		$798.5170	$798.53	$798.55	$798.50