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	$40.68	3.369%	$42.0505	$42.05	$42.05	$42.10
Purchase #2	$148.86	6.459%	$158.4749	$158.47	$158.45	$158.50
Purchase #3	$63.98	9.102%	$69.8035	$69.80	$69.80	$69.80
Purchase #4	$212.53	6.763%	$226.9034	$226.90	$226.90	$226.90
Purchase #5	$188.32	6.278%	$200.1427	$200.14	$200.15	$200.10
Purchase #6	$173.53	13.494%	$196.9461	$196.95	$196.95	$196.90
Purchase #7	$133.71	4.595%	$139.854	$139.85	$139.85	$139.90
7 purchase totals =	$961.61		$1,034.1751	$1,034.16	$1,034.15	$1,034.20