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	$81.51	10.456%	$90.0327	$90.03	$90.05	$90.00
Purchase #2	$71.91	12.569%	$80.9484	$80.95	$80.95	$80.90
Purchase #3	$56.86	5.200%	$59.8167	$59.82	$59.80	$59.80
Purchase #4	$51.89	7.166%	$55.6084	$55.61	$55.60	$55.60
Purchase #5	$28.57	11.416%	$31.8316	$31.83	$31.85	$31.80
Purchase #6	$130.82	4.206%	$136.3223	$136.32	$136.30	$136.30
Purchase #7	$164.78	6.346%	$175.2369	$175.24	$175.25	$175.20
7 purchase totals =	$586.34		$629.7970	$629.80	$629.80	$629.60