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	$20.97	3.790%	$21.7648	$21.76	$21.75	$21.80
Purchase #2	$114.92	10.262%	$126.7131	$126.71	$126.70	$126.70
Purchase #3	$89.46	11.458%	$99.7103	$99.71	$99.70	$99.70
Purchase #4	$116.30	10.798%	$128.8581	$128.86	$128.85	$128.90
Purchase #5	$221.83	9.740%	$243.4362	$243.44	$243.45	$243.40
Purchase #6	$140.33	9.845%	$154.1455	$154.15	$154.15	$154.10
Purchase #7	$146.96	11.786%	$164.2807	$164.28	$164.30	$164.30
7 purchase totals =	$850.77		$938.9087	$938.91	$938.90	$938.90