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	$84.65	7.256%	$90.7922	$90.79	$90.80	$90.80
Purchase #2	$146.33	12.720%	$164.9432	$164.94	$164.95	$164.90
Purchase #3	$142.85	9.505%	$156.4279	$156.43	$156.45	$156.40
Purchase #4	$218.36	9.594%	$239.3095	$239.31	$239.30	$239.30
Purchase #5	$224.56	11.637%	$250.692	$250.69	$250.70	$250.70
Purchase #6	$228.40	4.420%	$238.4953	$238.50	$238.50	$238.50
Purchase #7	$50.94	4.792%	$53.381	$53.38	$53.40	$53.40
7 purchase totals =	$1,096.09		$1,194.0411	$1,194.04	$1,194.10	$1,194.00