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	$72.37	10.582%	$80.0282	$80.03	$80.05	$80.00
Purchase #2	$90.70	9.521%	$99.3355	$99.34	$99.35	$99.30
Purchase #3	$107.52	5.616%	$113.5583	$113.56	$113.55	$113.60
Purchase #4	$70.46	3.199%	$72.714	$72.71	$72.70	$72.70
Purchase #5	$226.37	10.767%	$250.7433	$250.74	$250.75	$250.70
Purchase #6	$231.43	4.548%	$241.9554	$241.96	$241.95	$242.00
Purchase #7	$62.66	3.432%	$64.8105	$64.81	$64.80	$64.80
7 purchase totals =	$861.51		$923.1452	$923.15	$923.15	$923.10