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	$44.55	13.844%	$50.7175	$50.72	$50.70	$50.70
Purchase #2	$89.48	8.873%	$97.4196	$97.42	$97.40	$97.40
Purchase #3	$40.64	9.776%	$44.613	$44.61	$44.60	$44.60
Purchase #4	$31.65	3.535%	$32.7688	$32.77	$32.75	$32.80
Purchase #5	$173.30	13.115%	$196.0283	$196.03	$196.05	$196.00
Purchase #6	$33.67	11.805%	$37.6447	$37.64	$37.65	$37.60
Purchase #7	$132.44	13.179%	$149.8943	$149.89	$149.90	$149.90
7 purchase totals =	$545.73		$609.0862	$609.08	$609.05	$609.00