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	$31.80	8.518%	$34.5087	$34.51	$34.50	$34.50
Purchase #2	$242.25	5.373%	$255.2661	$255.27	$255.25	$255.30
Purchase #3	$50.44	9.458%	$55.2106	$55.21	$55.20	$55.20
Purchase #4	$134.75	11.331%	$150.0185	$150.02	$150.00	$150.00
Purchase #5	$41.45	3.872%	$43.0549	$43.05	$43.05	$43.10
Purchase #6	$94.34	6.630%	$100.5947	$100.59	$100.60	$100.60
Purchase #7	$64.27	5.589%	$67.8621	$67.86	$67.85	$67.90
7 purchase totals =	$659.30		$706.5156	$706.51	$706.45	$706.60