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	$19.76	3.869%	$20.5245	$20.52	$20.50	$20.50
Purchase #2	$145.68	4.829%	$152.7149	$152.71	$152.70	$152.70
Purchase #3	$205.84	10.359%	$227.163	$227.16	$227.15	$227.20
Purchase #4	$86.31	11.840%	$96.5291	$96.53	$96.55	$96.50
Purchase #5	$62.56	7.117%	$67.0124	$67.01	$67.00	$67.00
Purchase #6	$30.85	9.819%	$33.8792	$33.88	$33.90	$33.90
Purchase #7	$6.93	8.559%	$7.5231	$7.52	$7.50	$7.50
7 purchase totals =	$557.93		$605.3462	$605.33	$605.30	$605.30