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	$40.44	5.772%	$42.7742	$42.77	$42.75	$42.80
Purchase #2	$180.72	8.557%	$196.1842	$196.18	$196.20	$196.20
Purchase #3	$200.66	6.165%	$213.0307	$213.03	$213.05	$213.00
Purchase #4	$51.73	13.237%	$58.5775	$58.58	$58.60	$58.60
Purchase #5	$53.57	5.673%	$56.609	$56.61	$56.60	$56.60
Purchase #6	$228.73	12.205%	$256.6465	$256.65	$256.65	$256.60
Purchase #7	$96.68	13.313%	$109.551	$109.55	$109.55	$109.60
7 purchase totals =	$852.53		$933.3731	$933.37	$933.40	$933.40