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	$204.92	6.474%	$218.1865	$218.19	$218.20	$218.20
Purchase #2	$182.98	7.446%	$196.6047	$196.60	$196.60	$196.60
Purchase #3	$143.93	6.202%	$152.8565	$152.86	$152.85	$152.90
Purchase #4	$51.82	9.449%	$56.7165	$56.72	$56.70	$56.70
Purchase #5	$73.71	3.109%	$76.0016	$76.00	$76.00	$76.00
Purchase #6	$23.56	9.762%	$25.8599	$25.86	$25.85	$25.90
Purchase #7	$165.82	3.414%	$171.4811	$171.48	$171.50	$171.50
7 purchase totals =	$846.74		$897.7068	$897.71	$897.70	$897.80