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	$82.80	9.436%	$90.613	$90.61	$90.60	$90.60
Purchase #2	$84.37	4.132%	$87.8562	$87.86	$87.85	$87.90
Purchase #3	$50.77	13.145%	$57.4437	$57.44	$57.45	$57.40
Purchase #4	$112.91	7.108%	$120.9356	$120.94	$120.95	$120.90
Purchase #5	$218.73	9.103%	$238.641	$238.64	$238.65	$238.60
Purchase #6	$30.94	6.659%	$33.0003	$33.00	$33.00	$33.00
Purchase #7	$148.42	11.437%	$165.3948	$165.39	$165.40	$165.40
7 purchase totals =	$728.94		$793.8846	$793.88	$793.90	$793.80