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	$63.79	6.315%	$67.8183	$67.82	$67.80	$67.80
Purchase #2	$140.93	11.787%	$157.5414	$157.54	$157.55	$157.50
Purchase #3	$41.84	8.242%	$45.2885	$45.29	$45.30	$45.30
Purchase #4	$129.88	3.769%	$134.7752	$134.78	$134.80	$134.80
Purchase #5	$70.71	11.457%	$78.8112	$78.81	$78.80	$78.80
Purchase #6	$10.32	13.790%	$11.7431	$11.74	$11.75	$11.70
Purchase #7	$158.56	8.332%	$171.7712	$171.77	$171.75	$171.80
7 purchase totals =	$616.03		$667.7489	$667.75	$667.75	$667.70