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	$28.80	5.441%	$30.367	$30.37	$30.35	$30.40
Purchase #2	$40.54	11.799%	$45.3233	$45.32	$45.30	$45.30
Purchase #3	$82.43	12.294%	$92.5639	$92.56	$92.55	$92.60
Purchase #4	$25.93	11.457%	$28.9008	$28.90	$28.90	$28.90
Purchase #5	$60.50	10.822%	$67.0473	$67.05	$67.05	$67.00
Purchase #6	$22.39	6.302%	$23.801	$23.80	$23.80	$23.80
Purchase #7	$102.66	8.848%	$111.7434	$111.74	$111.75	$111.70
7 purchase totals =	$363.25		$399.7467	$399.74	$399.70	$399.70