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	$33.66	10.312%	$37.131	$37.13	$37.15	$37.10
Purchase #2	$105.81	5.765%	$111.9099	$111.91	$111.90	$111.90
Purchase #3	$25.48	13.305%	$28.8701	$28.87	$28.85	$28.90
Purchase #4	$61.64	7.264%	$66.1175	$66.12	$66.10	$66.10
Purchase #5	$83.44	6.581%	$88.9312	$88.93	$88.95	$88.90
Purchase #6	$201.74	11.122%	$224.1775	$224.18	$224.20	$224.20
Purchase #7	$73.35	10.439%	$81.007	$81.01	$81.00	$81.00
7 purchase totals =	$585.12		$638.1442	$638.15	$638.15	$638.10