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	$45.56	12.179%	$51.1088	$51.11	$51.10	$51.10
Purchase #2	$198.49	9.104%	$216.5605	$216.56	$216.55	$216.60
Purchase #3	$67.27	6.717%	$71.7885	$71.79	$71.80	$71.80
Purchase #4	$48.29	12.566%	$54.3581	$54.36	$54.35	$54.40
Purchase #5	$76.38	9.553%	$83.6766	$83.68	$83.70	$83.70
Purchase #6	$150.32	10.364%	$165.8992	$165.90	$165.90	$165.90
Purchase #7	$110.42	8.277%	$119.5595	$119.56	$119.55	$119.60
7 purchase totals =	$696.73		$762.9512	$762.96	$762.95	$763.10