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	$133.31	6.810%	$142.3884	$142.39	$142.40	$142.40
Purchase #2	$68.70	5.836%	$72.7093	$72.71	$72.70	$72.70
Purchase #3	$32.56	7.739%	$35.0798	$35.08	$35.10	$35.10
Purchase #4	$55.33	10.677%	$61.2376	$61.24	$61.25	$61.20
Purchase #5	$207.67	10.534%	$229.546	$229.55	$229.55	$229.50
Purchase #6	$243.49	10.649%	$269.4193	$269.42	$269.40	$269.40
Purchase #7	$86.26	4.460%	$90.1072	$90.11	$90.10	$90.10
7 purchase totals =	$827.32		$900.4876	$900.50	$900.50	$900.40