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	$35.93	7.361%	$38.5748	$38.57	$38.55	$38.60
Purchase #2	$180.69	10.478%	$199.6227	$199.62	$199.60	$199.60
Purchase #3	$108.98	6.591%	$116.1629	$116.16	$116.15	$116.20
Purchase #4	$41.43	9.643%	$45.4251	$45.43	$45.45	$45.40
Purchase #5	$241.28	6.351%	$256.6037	$256.60	$256.60	$256.60
Purchase #6	$54.43	5.483%	$57.4144	$57.41	$57.40	$57.40
Purchase #7	$195.91	6.751%	$209.1359	$209.14	$209.15	$209.10
7 purchase totals =	$858.65		$922.9395	$922.93	$922.90	$922.90