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	$173.50	5.798%	$183.5595	$183.56	$183.55	$183.60
Purchase #2	$114.86	9.462%	$125.7281	$125.73	$125.75	$125.70
Purchase #3	$200.30	12.233%	$224.8027	$224.80	$224.80	$224.80
Purchase #4	$131.37	3.636%	$136.1466	$136.15	$136.15	$136.10
Purchase #5	$141.32	6.592%	$150.6358	$150.64	$150.65	$150.60
Purchase #6	$205.46	5.287%	$216.3227	$216.32	$216.30	$216.30
Purchase #7	$12.69	5.649%	$13.4069	$13.41	$13.40	$13.40
7 purchase totals =	$979.50		$1,050.6023	$1,050.61	$1,050.60	$1,050.50