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	$16.90	9.524%	$18.5096	$18.51	$18.50	$18.50
Purchase #2	$30.77	5.277%	$32.3937	$32.39	$32.40	$32.40
Purchase #3	$180.34	9.145%	$196.8321	$196.83	$196.85	$196.80
Purchase #4	$69.30	3.804%	$71.9362	$71.94	$71.95	$71.90
Purchase #5	$78.61	5.330%	$82.7999	$82.80	$82.80	$82.80
Purchase #6	$51.43	13.117%	$58.1761	$58.18	$58.20	$58.20
Purchase #7	$124.52	3.168%	$128.4648	$128.46	$128.45	$128.50
7 purchase totals =	$551.87		$589.1124	$589.11	$589.15	$589.10