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	$243.87	10.578%	$269.6666	$269.67	$269.65	$269.70
Purchase #2	$58.46	10.227%	$64.4387	$64.44	$64.45	$64.40
Purchase #3	$203.52	4.237%	$212.1431	$212.14	$212.15	$212.10
Purchase #4	$139.73	5.648%	$147.622	$147.62	$147.60	$147.60
Purchase #5	$125.77	5.275%	$132.4044	$132.40	$132.40	$132.40
Purchase #6	$109.87	12.659%	$123.7784	$123.78	$123.80	$123.80
Purchase #7	$52.45	13.470%	$59.515	$59.52	$59.50	$59.50
7 purchase totals =	$933.67		$1,009.5682	$1,009.57	$1,009.55	$1,009.50