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	$202.44	9.587%	$221.8479	$221.85	$221.85	$221.80
Purchase #2	$49.93	4.599%	$52.2263	$52.23	$52.25	$52.20
Purchase #3	$240.41	12.608%	$270.7209	$270.72	$270.70	$270.70
Purchase #4	$218.66	4.539%	$228.585	$228.59	$228.60	$228.60
Purchase #5	$250.57	9.293%	$273.8555	$273.86	$273.85	$273.90
Purchase #6	$20.32	8.110%	$21.968	$21.97	$21.95	$22.00
Purchase #7	$69.65	4.665%	$72.8992	$72.90	$72.90	$72.90
7 purchase totals =	$1,051.98		$1,142.1028	$1,142.12	$1,142.10	$1,142.10