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	$65.81	3.127%	$67.8679	$67.87	$67.85	$67.90
Purchase #2	$12.81	8.226%	$13.8638	$13.86	$13.85	$13.90
Purchase #3	$64.59	9.874%	$70.9676	$70.97	$70.95	$71.00
Purchase #4	$64.76	9.287%	$70.7743	$70.77	$70.75	$70.80
Purchase #5	$100.77	11.188%	$112.0441	$112.04	$112.05	$112.00
Purchase #6	$31.90	13.871%	$36.3248	$36.32	$36.30	$36.30
Purchase #7	$120.65	6.187%	$128.1146	$128.11	$128.10	$128.10
7 purchase totals =	$461.29		$499.9571	$499.94	$499.85	$500.00