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	$20.91	4.214%	$21.7911	$21.79	$21.80	$21.80
Purchase #2	$61.39	4.715%	$64.2845	$64.28	$64.30	$64.30
Purchase #3	$6.90	11.544%	$7.6965	$7.70	$7.70	$7.70
Purchase #4	$214.74	6.591%	$228.8935	$228.89	$228.90	$228.90
Purchase #5	$32.57	5.646%	$34.4089	$34.41	$34.40	$34.40
Purchase #6	$11.96	10.556%	$13.2225	$13.22	$13.20	$13.20
Purchase #7	$40.33	5.600%	$42.5885	$42.59	$42.60	$42.60
7 purchase totals =	$388.80		$412.8855	$412.88	$412.90	$412.90