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	$38.30	11.696%	$42.7796	$42.78	$42.80	$42.80
Purchase #2	$201.76	11.764%	$225.495	$225.50	$225.50	$225.50
Purchase #3	$72.77	11.690%	$81.2768	$81.28	$81.30	$81.30
Purchase #4	$97.95	7.434%	$105.2316	$105.23	$105.25	$105.20
Purchase #5	$88.52	7.732%	$95.3644	$95.36	$95.35	$95.40
Purchase #6	$98.74	10.537%	$109.1442	$109.14	$109.15	$109.10
Purchase #7	$214.47	4.513%	$224.149	$224.15	$224.15	$224.10
7 purchase totals =	$812.51		$883.4406	$883.44	$883.50	$883.40