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	$110.43	8.560%	$119.8828	$119.88	$119.90	$119.90
Purchase #2	$143.53	7.623%	$154.4713	$154.47	$154.45	$154.50
Purchase #3	$44.85	5.336%	$47.2432	$47.24	$47.25	$47.20
Purchase #4	$190.90	5.244%	$200.9108	$200.91	$200.90	$200.90
Purchase #5	$111.47	5.761%	$117.8918	$117.89	$117.90	$117.90
Purchase #6	$240.51	11.616%	$268.4476	$268.45	$268.45	$268.40
Purchase #7	$85.57	5.670%	$90.4218	$90.42	$90.40	$90.40
7 purchase totals =	$927.26		$999.2693	$999.26	$999.25	$999.20