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	$72.79	13.115%	$82.3364	$82.34	$82.35	$82.30
Purchase #2	$141.46	10.781%	$156.7108	$156.71	$156.70	$156.70
Purchase #3	$86.43	10.119%	$95.1759	$95.18	$95.20	$95.20
Purchase #4	$34.46	13.597%	$39.1455	$39.15	$39.15	$39.10
Purchase #5	$117.82	11.559%	$131.4388	$131.44	$131.45	$131.40
Purchase #6	$62.76	9.830%	$68.9293	$68.93	$68.95	$68.90
Purchase #7	$104.89	7.859%	$113.1333	$113.13	$113.15	$113.10
7 purchase totals =	$620.61		$686.8700	$686.88	$686.95	$686.70