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	$245.78	13.835%	$279.7837	$279.78	$279.80	$279.80
Purchase #2	$209.68	4.587%	$219.298	$219.30	$219.30	$219.30
Purchase #3	$80.37	3.384%	$83.0897	$83.09	$83.10	$83.10
Purchase #4	$123.88	11.251%	$137.8177	$137.82	$137.80	$137.80
Purchase #5	$202.43	13.371%	$229.4969	$229.50	$229.50	$229.50
Purchase #6	$128.70	8.465%	$139.5945	$139.59	$139.60	$139.60
Purchase #7	$137.32	10.684%	$151.9913	$151.99	$152.00	$152.00
7 purchase totals =	$1,128.16		$1,241.0718	$1,241.07	$1,241.10	$1,241.10