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	$30.36	11.210%	$33.7634	$33.76	$33.75	$33.80
Purchase #2	$53.97	10.673%	$59.7302	$59.73	$59.75	$59.70
Purchase #3	$102.95	6.305%	$109.441	$109.44	$109.45	$109.40
Purchase #4	$248.41	9.835%	$272.8411	$272.84	$272.85	$272.80
Purchase #5	$101.62	7.659%	$109.4031	$109.40	$109.40	$109.40
Purchase #6	$175.46	5.667%	$185.4033	$185.40	$185.40	$185.40
Purchase #7	$62.34	8.392%	$67.5716	$67.57	$67.55	$67.60
7 purchase totals =	$775.11		$838.1537	$838.14	$838.15	$838.10