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	$99.56	9.563%	$109.0809	$109.08	$109.10	$109.10
Purchase #2	$19.32	12.836%	$21.7999	$21.80	$21.80	$21.80
Purchase #3	$5.52	11.614%	$6.1611	$6.16	$6.15	$6.20
Purchase #4	$69.98	11.632%	$78.1201	$78.12	$78.10	$78.10
Purchase #5	$147.72	12.702%	$166.4834	$166.48	$166.50	$166.50
Purchase #6	$81.69	12.635%	$92.0115	$92.01	$92.00	$92.00
Purchase #7	$64.61	5.765%	$68.3348	$68.33	$68.35	$68.30
7 purchase totals =	$488.40		$541.9917	$541.98	$542.00	$542.00