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	$81.37	9.546%	$89.1376	$89.14	$89.15	$89.10
Purchase #2	$26.33	5.664%	$27.8213	$27.82	$27.80	$27.80
Purchase #3	$95.48	13.663%	$108.5254	$108.53	$108.55	$108.50
Purchase #4	$145.89	4.484%	$152.4317	$152.43	$152.45	$152.40
Purchase #5	$151.51	7.262%	$162.5127	$162.51	$162.50	$162.50
Purchase #6	$5.61	9.725%	$6.1556	$6.16	$6.15	$6.20
Purchase #7	$46.63	12.603%	$52.5068	$52.51	$52.50	$52.50
7 purchase totals =	$552.82		$599.0911	$599.10	$599.10	$599.00