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	$50.45	5.569%	$53.2596	$53.26	$53.25	$53.30
Purchase #2	$37.92	3.679%	$39.3151	$39.32	$39.30	$39.30
Purchase #3	$137.49	7.158%	$147.3315	$147.33	$147.35	$147.30
Purchase #4	$189.84	5.565%	$200.4046	$200.40	$200.40	$200.40
Purchase #5	$169.59	8.615%	$184.2002	$184.20	$184.20	$184.20
Purchase #6	$115.54	3.277%	$119.3262	$119.33	$119.35	$119.30
Purchase #7	$72.83	10.434%	$80.4291	$80.43	$80.45	$80.40
7 purchase totals =	$773.66		$824.2663	$824.27	$824.30	$824.20