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	$79.32	5.748%	$83.8793	$83.88	$83.90	$83.90
Purchase #2	$217.49	5.427%	$229.2932	$229.29	$229.30	$229.30
Purchase #3	$152.40	12.174%	$170.9532	$170.95	$170.95	$171.00
Purchase #4	$57.58	12.359%	$64.6963	$64.70	$64.70	$64.70
Purchase #5	$37.90	6.419%	$40.3328	$40.33	$40.35	$40.30
Purchase #6	$165.95	11.523%	$185.0724	$185.07	$185.05	$185.10
Purchase #7	$71.97	13.360%	$81.5852	$81.59	$81.60	$81.60
7 purchase totals =	$782.61		$855.8124	$855.81	$855.85	$855.90