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	$84.83	7.870%	$91.5061	$91.51	$91.50	$91.50
Purchase #2	$180.52	6.337%	$191.9596	$191.96	$191.95	$192.00
Purchase #3	$164.53	11.434%	$183.3424	$183.34	$183.35	$183.30
Purchase #4	$29.32	10.343%	$32.3526	$32.35	$32.35	$32.40
Purchase #5	$28.27	11.478%	$31.5148	$31.51	$31.50	$31.50
Purchase #6	$66.26	5.522%	$69.9189	$69.92	$69.90	$69.90
Purchase #7	$218.86	11.554%	$244.1471	$244.15	$244.15	$244.10
7 purchase totals =	$772.59		$844.7415	$844.74	$844.70	$844.70