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	$82.27	9.473%	$90.0634	$90.06	$90.05	$90.10
Purchase #2	$96.84	6.199%	$102.8431	$102.84	$102.85	$102.80
Purchase #3	$242.65	12.751%	$273.5903	$273.59	$273.60	$273.60
Purchase #4	$79.95	9.482%	$87.5309	$87.53	$87.55	$87.50
Purchase #5	$138.58	5.154%	$145.7224	$145.72	$145.70	$145.70
Purchase #6	$36.86	12.377%	$41.4222	$41.42	$41.40	$41.40
Purchase #7	$66.56	7.249%	$71.3849	$71.38	$71.40	$71.40
7 purchase totals =	$743.71		$812.5572	$812.54	$812.55	$812.50