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	$28.27	12.131%	$31.6994	$31.70	$31.70	$31.70
Purchase #2	$186.77	6.458%	$198.8316	$198.83	$198.85	$198.80
Purchase #3	$167.55	10.701%	$185.4795	$185.48	$185.50	$185.50
Purchase #4	$86.55	6.110%	$91.8382	$91.84	$91.85	$91.80
Purchase #5	$150.31	10.413%	$165.9618	$165.96	$165.95	$166.00
Purchase #6	$81.79	8.178%	$88.4788	$88.48	$88.50	$88.50
Purchase #7	$205.60	8.188%	$222.4345	$222.43	$222.45	$222.40
7 purchase totals =	$906.84		$984.7238	$984.72	$984.80	$984.70