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	$178.82	3.812%	$185.6366	$185.64	$185.65	$185.60
Purchase #2	$243.95	8.349%	$264.3174	$264.32	$264.30	$264.30
Purchase #3	$132.77	11.667%	$148.2603	$148.26	$148.25	$148.30
Purchase #4	$144.99	13.184%	$164.1055	$164.11	$164.10	$164.10
Purchase #5	$82.99	9.415%	$90.8035	$90.80	$90.80	$90.80
Purchase #6	$79.91	7.424%	$85.8425	$85.84	$85.85	$85.80
Purchase #7	$133.57	8.746%	$145.252	$145.25	$145.25	$145.30
7 purchase totals =	$997.00		$1,084.2178	$1,084.22	$1,084.20	$1,084.20