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	$33.86	13.209%	$38.3326	$38.33	$38.35	$38.30
Purchase #2	$39.65	12.580%	$44.638	$44.64	$44.65	$44.60
Purchase #3	$38.72	9.352%	$42.3411	$42.34	$42.35	$42.30
Purchase #4	$89.48	6.701%	$95.4761	$95.48	$95.50	$95.50
Purchase #5	$118.36	8.507%	$128.4289	$128.43	$128.45	$128.40
Purchase #6	$81.66	5.414%	$86.0811	$86.08	$86.10	$86.10
Purchase #7	$17.43	11.721%	$19.473	$19.47	$19.45	$19.50
7 purchase totals =	$419.16		$454.7708	$454.77	$454.85	$454.70