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	$39.44	10.352%	$43.5228	$43.52	$43.50	$43.50
Purchase #2	$37.80	13.609%	$42.9442	$42.94	$42.95	$42.90
Purchase #3	$84.57	9.119%	$92.2819	$92.28	$92.30	$92.30
Purchase #4	$196.56	13.854%	$223.7914	$223.79	$223.80	$223.80
Purchase #5	$170.37	6.608%	$181.628	$181.63	$181.65	$181.60
Purchase #6	$13.46	9.338%	$14.7169	$14.72	$14.70	$14.70
Purchase #7	$51.43	12.556%	$57.8876	$57.89	$57.90	$57.90
7 purchase totals =	$593.63		$656.7728	$656.77	$656.80	$656.70