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	$197.85	13.273%	$224.1106	$224.11	$224.10	$224.10
Purchase #2	$96.99	6.695%	$103.4835	$103.48	$103.50	$103.50
Purchase #3	$90.51	13.202%	$102.4591	$102.46	$102.45	$102.50
Purchase #4	$204.50	3.345%	$211.3405	$211.34	$211.35	$211.30
Purchase #5	$160.33	4.401%	$167.3861	$167.39	$167.40	$167.40
Purchase #6	$28.56	11.249%	$31.7727	$31.77	$31.75	$31.80
Purchase #7	$76.86	4.475%	$80.2995	$80.30	$80.30	$80.30
7 purchase totals =	$855.60		$920.8520	$920.85	$920.85	$920.90