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	$236.80	11.126%	$263.1464	$263.15	$263.15	$263.10
Purchase #2	$176.90	3.680%	$183.4099	$183.41	$183.40	$183.40
Purchase #3	$176.56	11.223%	$196.3753	$196.38	$196.40	$196.40
Purchase #4	$170.89	6.217%	$181.5142	$181.51	$181.50	$181.50
Purchase #5	$179.25	7.681%	$193.0182	$193.02	$193.00	$193.00
Purchase #6	$168.27	12.190%	$188.7821	$188.78	$188.80	$188.80
Purchase #7	$133.65	7.230%	$143.3129	$143.31	$143.30	$143.30
7 purchase totals =	$1,242.32		$1,349.5590	$1,349.56	$1,349.55	$1,349.50