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	$71.32	6.734%	$76.1227	$76.12	$76.10	$76.10
Purchase #2	$138.95	6.260%	$147.6483	$147.65	$147.65	$147.60
Purchase #3	$22.95	12.721%	$25.8695	$25.87	$25.85	$25.90
Purchase #4	$235.54	11.620%	$262.9097	$262.91	$262.90	$262.90
Purchase #5	$99.45	13.482%	$112.8578	$112.86	$112.85	$112.90
Purchase #6	$40.27	6.716%	$42.9745	$42.97	$42.95	$43.00
Purchase #7	$210.52	3.802%	$218.524	$218.52	$218.50	$218.50
7 purchase totals =	$819.00		$886.9065	$886.90	$886.80	$886.90