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	$81.99	9.657%	$89.9078	$89.91	$89.90	$89.90
Purchase #2	$169.37	12.378%	$190.3346	$190.33	$190.35	$190.30
Purchase #3	$175.53	13.734%	$199.6373	$199.64	$199.65	$199.60
Purchase #4	$98.37	7.486%	$105.734	$105.73	$105.75	$105.70
Purchase #5	$39.92	13.619%	$45.3567	$45.36	$45.35	$45.40
Purchase #6	$223.41	7.719%	$240.655	$240.66	$240.65	$240.70
Purchase #7	$250.68	11.766%	$280.175	$280.18	$280.20	$280.20
7 purchase totals =	$1,039.27		$1,151.8004	$1,151.81	$1,151.85	$1,151.80