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	$159.85	12.337%	$179.5707	$179.57	$179.55	$179.60
Purchase #2	$169.74	3.543%	$175.7539	$175.75	$175.75	$175.80
Purchase #3	$94.35	6.563%	$100.5422	$100.54	$100.55	$100.50
Purchase #4	$246.83	13.480%	$280.1027	$280.10	$280.10	$280.10
Purchase #5	$166.69	9.308%	$182.2055	$182.21	$182.20	$182.20
Purchase #6	$129.31	6.507%	$137.7242	$137.72	$137.70	$137.70
Purchase #7	$56.92	4.142%	$59.2776	$59.28	$59.30	$59.30
7 purchase totals =	$1,023.69		$1,115.1768	$1,115.17	$1,115.15	$1,115.20