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	$96.55	10.426%	$106.6163	$106.62	$106.60	$106.60
Purchase #2	$73.37	9.398%	$80.2653	$80.27	$80.25	$80.30
Purchase #3	$158.79	6.140%	$168.5397	$168.54	$168.55	$168.50
Purchase #4	$90.43	7.173%	$96.9165	$96.92	$96.90	$96.90
Purchase #5	$50.82	5.285%	$53.5058	$53.51	$53.50	$53.50
Purchase #6	$232.93	5.374%	$245.4477	$245.45	$245.45	$245.40
Purchase #7	$137.59	7.564%	$147.9973	$148.00	$148.00	$148.00
7 purchase totals =	$840.48		$899.2886	$899.31	$899.25	$899.20