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	$86.71	5.571%	$91.5406	$91.54	$91.55	$91.50
Purchase #2	$227.54	6.283%	$241.8363	$241.84	$241.85	$241.80
Purchase #3	$37.65	12.721%	$42.4395	$42.44	$42.45	$42.40
Purchase #4	$94.34	4.236%	$98.3362	$98.34	$98.35	$98.30
Purchase #5	$83.61	9.382%	$91.4543	$91.45	$91.45	$91.50
Purchase #6	$125.80	4.597%	$131.583	$131.58	$131.60	$131.60
Purchase #7	$222.83	3.181%	$229.9182	$229.92	$229.90	$229.90
7 purchase totals =	$878.48		$927.1081	$927.11	$927.15	$927.00