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	$99.57	11.606%	$111.1261	$111.13	$111.15	$111.10
Purchase #2	$141.76	10.250%	$156.2904	$156.29	$156.30	$156.30
Purchase #3	$91.93	3.809%	$95.4316	$95.43	$95.45	$95.40
Purchase #4	$107.30	9.805%	$117.8208	$117.82	$117.80	$117.80
Purchase #5	$147.70	11.864%	$165.2231	$165.22	$165.20	$165.20
Purchase #6	$112.35	12.601%	$126.5072	$126.51	$126.50	$126.50
Purchase #7	$7.48	12.230%	$8.3948	$8.39	$8.40	$8.40
7 purchase totals =	$708.09		$780.7940	$780.79	$780.80	$780.70