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	$115.45	11.584%	$128.8237	$128.82	$128.80	$128.80
Purchase #2	$79.63	11.281%	$88.6131	$88.61	$88.60	$88.60
Purchase #3	$123.56	7.547%	$132.8851	$132.89	$132.90	$132.90
Purchase #4	$210.69	6.444%	$224.2669	$224.27	$224.25	$224.30
Purchase #5	$101.80	9.424%	$111.3936	$111.39	$111.40	$111.40
Purchase #6	$28.41	5.806%	$30.0595	$30.06	$30.05	$30.10
Purchase #7	$93.87	11.132%	$104.3196	$104.32	$104.30	$104.30
7 purchase totals =	$753.41		$820.3615	$820.36	$820.30	$820.40