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	$122.94	9.828%	$135.0225	$135.02	$135.00	$135.00
Purchase #2	$79.74	13.187%	$90.2553	$90.26	$90.25	$90.30
Purchase #3	$210.89	7.695%	$227.118	$227.12	$227.10	$227.10
Purchase #4	$100.95	7.478%	$108.499	$108.50	$108.50	$108.50
Purchase #5	$159.97	4.331%	$166.8983	$166.90	$166.90	$166.90
Purchase #6	$66.96	7.264%	$71.824	$71.82	$71.80	$71.80
Purchase #7	$152.89	7.328%	$164.0938	$164.09	$164.10	$164.10
7 purchase totals =	$894.34		$963.7109	$963.71	$963.65	$963.70