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	$170.51	11.493%	$190.1067	$190.11	$190.10	$190.10
Purchase #2	$78.84	9.824%	$86.5852	$86.59	$86.60	$86.60
Purchase #3	$218.32	12.635%	$245.9047	$245.90	$245.90	$245.90
Purchase #4	$58.32	8.547%	$63.3046	$63.30	$63.30	$63.30
Purchase #5	$50.69	6.262%	$53.8642	$53.86	$53.85	$53.90
Purchase #6	$61.72	11.690%	$68.9351	$68.94	$68.95	$68.90
Purchase #7	$218.45	7.185%	$234.1456	$234.15	$234.15	$234.10
7 purchase totals =	$856.85		$942.8461	$942.85	$942.85	$942.80