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	$86.48	13.771%	$98.3892	$98.39	$98.40	$98.40
Purchase #2	$38.77	10.345%	$42.7808	$42.78	$42.80	$42.80
Purchase #3	$87.91	3.853%	$91.2972	$91.30	$91.30	$91.30
Purchase #4	$83.81	13.796%	$95.3724	$95.37	$95.35	$95.40
Purchase #5	$165.39	7.778%	$178.254	$178.25	$178.25	$178.30
Purchase #6	$72.81	8.129%	$78.7287	$78.73	$78.75	$78.70
Purchase #7	$25.27	12.426%	$28.4101	$28.41	$28.40	$28.40
7 purchase totals =	$560.44		$613.2324	$613.23	$613.25	$613.30