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	4.751%	$21.9663	$21.97	$21.95	$22.00
Purchase #2	$169.74	12.835%	$191.5261	$191.53	$191.55	$191.50
Purchase #3	$148.29	4.684%	$155.2359	$155.24	$155.25	$155.20
Purchase #4	$99.46	11.412%	$110.8104	$110.81	$110.80	$110.80
Purchase #5	$36.55	9.813%	$40.1367	$40.14	$40.15	$40.10
Purchase #6	$84.91	11.153%	$94.38	$94.38	$94.40	$94.40
Purchase #7	$100.95	10.758%	$111.8102	$111.81	$111.80	$111.80
7 purchase totals =	$660.87		$725.8656	$725.88	$725.90	$725.80