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	$33.92	5.783%	$35.8816	$35.88	$35.90	$35.90
Purchase #2	$19.35	10.518%	$21.3852	$21.39	$21.40	$21.40
Purchase #3	$115.27	11.422%	$128.4361	$128.44	$128.45	$128.40
Purchase #4	$116.43	4.129%	$121.2374	$121.24	$121.25	$121.20
Purchase #5	$74.85	7.518%	$80.4772	$80.48	$80.50	$80.50
Purchase #6	$85.77	4.865%	$89.9427	$89.94	$89.95	$89.90
Purchase #7	$7.98	6.227%	$8.4769	$8.48	$8.50	$8.50
7 purchase totals =	$453.57		$485.8371	$485.85	$485.95	$485.80