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	$84.36	6.521%	$89.8611	$89.86	$89.85	$89.90
Purchase #2	$80.58	8.820%	$87.6872	$87.69	$87.70	$87.70
Purchase #3	$161.82	3.740%	$167.8721	$167.87	$167.85	$167.90
Purchase #4	$133.73	12.680%	$150.687	$150.69	$150.70	$150.70
Purchase #5	$157.37	13.763%	$179.0288	$179.03	$179.05	$179.00
Purchase #6	$166.72	11.354%	$185.6494	$185.65	$185.65	$185.60
Purchase #7	$161.99	11.301%	$180.2965	$180.30	$180.30	$180.30
7 purchase totals =	$946.57		$1,041.0821	$1,041.09	$1,041.10	$1,041.10