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	$226.87	10.476%	$250.6369	$250.64	$250.65	$250.60
Purchase #2	$46.59	10.134%	$51.3114	$51.31	$51.30	$51.30
Purchase #3	$133.79	9.619%	$146.6593	$146.66	$146.65	$146.70
Purchase #4	$30.33	8.522%	$32.9147	$32.91	$32.90	$32.90
Purchase #5	$143.89	13.515%	$163.3367	$163.34	$163.35	$163.30
Purchase #6	$156.25	5.269%	$164.4828	$164.48	$164.50	$164.50
Purchase #7	$235.72	11.805%	$263.5467	$263.55	$263.55	$263.50
7 purchase totals =	$973.44		$1,072.8885	$1,072.89	$1,072.90	$1,072.80