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	$121.56	13.441%	$137.8989	$137.90	$137.90	$137.90
Purchase #2	$228.81	7.426%	$245.8014	$245.80	$245.80	$245.80
Purchase #3	$146.65	12.254%	$164.6205	$164.62	$164.60	$164.60
Purchase #4	$161.53	12.700%	$182.0443	$182.04	$182.05	$182.00
Purchase #5	$147.68	9.174%	$161.2282	$161.23	$161.25	$161.20
Purchase #6	$81.28	4.725%	$85.1205	$85.12	$85.10	$85.10
Purchase #7	$83.58	7.658%	$89.9806	$89.98	$90.00	$90.00
7 purchase totals =	$971.09		$1,066.6944	$1,066.69	$1,066.70	$1,066.60