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	$243.34	6.488%	$259.1279	$259.13	$259.15	$259.10
Purchase #2	$128.30	10.592%	$141.8895	$141.89	$141.90	$141.90
Purchase #3	$142.81	6.776%	$152.4868	$152.49	$152.50	$152.50
Purchase #4	$50.26	11.300%	$55.9394	$55.94	$55.95	$55.90
Purchase #5	$102.68	3.488%	$106.2615	$106.26	$106.25	$106.30
Purchase #6	$159.74	13.381%	$181.1148	$181.11	$181.10	$181.10
Purchase #7	$89.40	5.678%	$94.4761	$94.48	$94.50	$94.50
7 purchase totals =	$916.53		$991.2960	$991.30	$991.35	$991.30