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	$77.88	5.420%	$82.1011	$82.10	$82.10	$82.10
Purchase #2	$58.45	9.107%	$63.773	$63.77	$63.75	$63.80
Purchase #3	$183.59	8.109%	$198.4773	$198.48	$198.50	$198.50
Purchase #4	$180.64	3.502%	$186.966	$186.97	$186.95	$187.00
Purchase #5	$33.94	9.351%	$37.1137	$37.11	$37.10	$37.10
Purchase #6	$90.97	10.337%	$100.3736	$100.37	$100.35	$100.40
Purchase #7	$210.39	3.340%	$217.417	$217.42	$217.40	$217.40
7 purchase totals =	$835.86		$886.2217	$886.22	$886.15	$886.30