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	$168.76	13.458%	$191.4717	$191.47	$191.45	$191.50
Purchase #2	$36.63	11.693%	$40.9131	$40.91	$40.90	$40.90
Purchase #3	$38.40	7.701%	$41.3572	$41.36	$41.35	$41.40
Purchase #4	$144.76	3.814%	$150.2811	$150.28	$150.30	$150.30
Purchase #5	$241.45	13.216%	$273.36	$273.36	$273.35	$273.40
Purchase #6	$86.73	4.239%	$90.4065	$90.41	$90.40	$90.40
Purchase #7	$173.27	9.581%	$189.871	$189.87	$189.85	$189.90
7 purchase totals =	$890.00		$977.6606	$977.66	$977.60	$977.80