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	$28.88	11.317%	$32.1483	$32.15	$32.15	$32.10
Purchase #2	$118.54	11.402%	$132.0559	$132.06	$132.05	$132.10
Purchase #3	$49.25	9.210%	$53.7859	$53.79	$53.80	$53.80
Purchase #4	$30.55	7.634%	$32.8822	$32.88	$32.90	$32.90
Purchase #5	$95.88	7.560%	$103.1285	$103.13	$103.15	$103.10
Purchase #6	$151.55	9.140%	$165.4017	$165.40	$165.40	$165.40
Purchase #7	$250.93	8.821%	$273.0645	$273.06	$273.05	$273.10
7 purchase totals =	$725.58		$792.4670	$792.47	$792.50	$792.50