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	$49.73	11.732%	$55.5643	$55.56	$55.55	$55.60
Purchase #2	$164.53	6.444%	$175.1323	$175.13	$175.15	$175.10
Purchase #3	$121.26	6.682%	$129.3626	$129.36	$129.35	$129.40
Purchase #4	$105.81	5.157%	$111.2666	$111.27	$111.25	$111.30
Purchase #5	$112.95	3.691%	$117.119	$117.12	$117.10	$117.10
Purchase #6	$82.82	13.689%	$94.1572	$94.16	$94.15	$94.20
Purchase #7	$104.46	11.730%	$116.7132	$116.71	$116.70	$116.70
7 purchase totals =	$741.56		$799.3152	$799.31	$799.25	$799.40