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	$67.41	6.540%	$71.8186	$71.82	$71.80	$71.80
Purchase #2	$80.70	13.341%	$91.4662	$91.47	$91.45	$91.50
Purchase #3	$140.27	11.190%	$155.9662	$155.97	$155.95	$156.00
Purchase #4	$185.91	5.632%	$196.3805	$196.38	$196.40	$196.40
Purchase #5	$220.97	13.319%	$250.401	$250.40	$250.40	$250.40
Purchase #6	$106.40	7.500%	$114.38	$114.38	$114.40	$114.40
Purchase #7	$37.50	6.687%	$40.0076	$40.01	$40.00	$40.00
7 purchase totals =	$839.16		$920.4201	$920.43	$920.40	$920.50