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	$147.98	12.779%	$166.8904	$166.89	$166.90	$166.90
Purchase #2	$244.34	8.387%	$264.8328	$264.83	$264.85	$264.80
Purchase #3	$206.70	11.232%	$229.9165	$229.92	$229.90	$229.90
Purchase #4	$84.60	11.631%	$94.4398	$94.44	$94.45	$94.40
Purchase #5	$174.29	3.494%	$180.3797	$180.38	$180.40	$180.40
Purchase #6	$56.69	6.177%	$60.1917	$60.19	$60.20	$60.20
Purchase #7	$91.76	9.278%	$100.2735	$100.27	$100.25	$100.30
7 purchase totals =	$1,006.36		$1,096.9244	$1,096.92	$1,096.95	$1,096.90