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	$5.61	3.612%	$5.8126	$5.81	$5.80	$5.80
Purchase #2	$207.87	12.495%	$233.8434	$233.84	$233.85	$233.80
Purchase #3	$78.85	4.144%	$82.1175	$82.12	$82.10	$82.10
Purchase #4	$42.84	12.770%	$48.3107	$48.31	$48.30	$48.30
Purchase #5	$196.87	4.797%	$206.3139	$206.31	$206.30	$206.30
Purchase #6	$200.96	10.709%	$222.4808	$222.48	$222.50	$222.50
Purchase #7	$92.80	13.670%	$105.4858	$105.49	$105.50	$105.50
7 purchase totals =	$825.80		$904.3647	$904.36	$904.35	$904.30