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	$81.44	9.802%	$89.4227	$89.42	$89.40	$89.40
Purchase #2	$21.38	10.185%	$23.5576	$23.56	$23.55	$23.60
Purchase #3	$84.51	6.859%	$90.3065	$90.31	$90.30	$90.30
Purchase #4	$191.87	11.124%	$213.2136	$213.21	$213.20	$213.20
Purchase #5	$91.34	10.118%	$100.5818	$100.58	$100.60	$100.60
Purchase #6	$196.94	3.749%	$204.3233	$204.32	$204.30	$204.30
Purchase #7	$169.61	13.481%	$192.4751	$192.48	$192.50	$192.50
7 purchase totals =	$837.09		$913.8806	$913.88	$913.85	$913.90