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	$80.48	13.381%	$91.249	$91.25	$91.25	$91.20
Purchase #2	$211.32	10.686%	$233.9017	$233.90	$233.90	$233.90
Purchase #3	$88.76	8.760%	$96.5354	$96.54	$96.55	$96.50
Purchase #4	$54.55	3.301%	$56.3507	$56.35	$56.35	$56.40
Purchase #5	$168.32	10.599%	$186.1602	$186.16	$186.15	$186.20
Purchase #6	$139.49	11.386%	$155.3723	$155.37	$155.35	$155.40
Purchase #7	$62.64	6.657%	$66.8099	$66.81	$66.80	$66.80
7 purchase totals =	$805.56		$886.3792	$886.38	$886.35	$886.40