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	$158.55	7.429%	$170.3287	$170.33	$170.35	$170.30
Purchase #2	$240.55	7.690%	$259.0483	$259.05	$259.05	$259.00
Purchase #3	$165.52	10.219%	$182.4345	$182.43	$182.45	$182.40
Purchase #4	$170.89	4.265%	$178.1785	$178.18	$178.20	$178.20
Purchase #5	$145.79	12.393%	$163.8578	$163.86	$163.85	$163.90
Purchase #6	$6.52	8.185%	$7.0537	$7.05	$7.05	$7.10
Purchase #7	$53.74	9.861%	$59.0393	$59.04	$59.05	$59.00
7 purchase totals =	$941.56		$1,019.9408	$1,019.94	$1,020.00	$1,019.90