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	$5.62	11.302%	$6.2552	$6.26	$6.25	$6.30
Purchase #2	$210.45	6.264%	$223.6326	$223.63	$223.65	$223.60
Purchase #3	$83.92	7.120%	$89.8951	$89.90	$89.90	$89.90
Purchase #4	$237.54	7.671%	$255.7617	$255.76	$255.75	$255.80
Purchase #5	$184.96	13.664%	$210.2329	$210.23	$210.25	$210.20
Purchase #6	$52.51	5.332%	$55.3098	$55.31	$55.30	$55.30
Purchase #7	$196.83	8.457%	$213.4759	$213.48	$213.50	$213.50
7 purchase totals =	$971.83		$1,054.5632	$1,054.57	$1,054.60	$1,054.60