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	$85.37	6.400%	$90.8337	$90.83	$90.85	$90.80
Purchase #2	$47.77	6.644%	$50.9438	$50.94	$50.95	$50.90
Purchase #3	$142.69	11.867%	$159.623	$159.62	$159.60	$159.60
Purchase #4	$227.96	4.735%	$238.7539	$238.75	$238.75	$238.80
Purchase #5	$116.53	4.492%	$121.7645	$121.76	$121.75	$121.80
Purchase #6	$128.47	10.806%	$142.3525	$142.35	$142.35	$142.40
Purchase #7	$32.97	11.870%	$36.8835	$36.88	$36.90	$36.90
7 purchase totals =	$781.76		$841.1549	$841.13	$841.15	$841.20