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	$58.72	5.109%	$61.72	$61.72	$61.70	$61.70
Purchase #2	$120.97	13.177%	$136.9102	$136.91	$136.90	$136.90
Purchase #3	$96.41	9.139%	$105.2209	$105.22	$105.20	$105.20
Purchase #4	$104.55	7.414%	$112.3013	$112.30	$112.30	$112.30
Purchase #5	$111.81	7.147%	$119.8011	$119.80	$119.80	$119.80
Purchase #6	$96.31	3.220%	$99.4112	$99.41	$99.40	$99.40
Purchase #7	$79.25	3.737%	$82.2116	$82.21	$82.20	$82.20
7 purchase totals =	$668.02		$717.5763	$717.57	$717.50	$717.50