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	$44.80	12.315%	$50.3171	$50.32	$50.30	$50.30
Purchase #2	$120.26	5.267%	$126.5941	$126.59	$126.60	$126.60
Purchase #3	$143.66	3.639%	$148.8878	$148.89	$148.90	$148.90
Purchase #4	$133.73	5.238%	$140.7348	$140.73	$140.75	$140.70
Purchase #5	$142.78	5.525%	$150.6686	$150.67	$150.65	$150.70
Purchase #6	$39.37	5.327%	$41.4672	$41.47	$41.45	$41.50
Purchase #7	$190.33	3.393%	$196.7879	$196.79	$196.80	$196.80
7 purchase totals =	$814.93		$855.4575	$855.46	$855.45	$855.50