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	$109.28	13.290%	$123.8033	$123.80	$123.80	$123.80
Purchase #2	$173.26	11.705%	$193.5401	$193.54	$193.55	$193.50
Purchase #3	$229.98	5.651%	$242.9762	$242.98	$243.00	$243.00
Purchase #4	$123.82	13.394%	$140.4045	$140.40	$140.40	$140.40
Purchase #5	$145.72	7.443%	$156.5659	$156.57	$156.55	$156.60
Purchase #6	$159.59	5.604%	$168.5334	$168.53	$168.55	$168.50
Purchase #7	$71.71	5.617%	$75.738	$75.74	$75.75	$75.70
7 purchase totals =	$1,013.36		$1,101.5614	$1,101.56	$1,101.60	$1,101.50