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	$210.55	5.871%	$222.9114	$222.91	$222.90	$222.90
Purchase #2	$193.86	12.115%	$217.3461	$217.35	$217.35	$217.30
Purchase #3	$49.29	10.460%	$54.4457	$54.45	$54.45	$54.40
Purchase #4	$66.85	6.854%	$71.4319	$71.43	$71.45	$71.40
Purchase #5	$163.41	10.512%	$180.5877	$180.59	$180.60	$180.60
Purchase #6	$24.58	12.483%	$27.6483	$27.65	$27.65	$27.60
Purchase #7	$53.76	11.379%	$59.8774	$59.88	$59.90	$59.90
7 purchase totals =	$762.30		$834.2485	$834.26	$834.30	$834.10