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	$34.30	10.316%	$37.8384	$37.84	$37.85	$37.80
Purchase #2	$29.36	13.208%	$33.2379	$33.24	$33.25	$33.20
Purchase #3	$232.95	3.266%	$240.5581	$240.56	$240.55	$240.60
Purchase #4	$100.27	10.646%	$110.9447	$110.94	$110.95	$110.90
Purchase #5	$19.32	7.675%	$20.8028	$20.80	$20.80	$20.80
Purchase #6	$96.64	9.559%	$105.8778	$105.88	$105.90	$105.90
Purchase #7	$38.29	11.809%	$42.8117	$42.81	$42.80	$42.80
7 purchase totals =	$551.13		$592.0714	$592.07	$592.10	$592.00