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	$25.82	5.414%	$27.2179	$27.22	$27.20	$27.20
Purchase #2	$39.33	7.369%	$42.2282	$42.23	$42.25	$42.20
Purchase #3	$45.83	10.432%	$50.611	$50.61	$50.60	$50.60
Purchase #4	$107.39	7.590%	$115.5409	$115.54	$115.55	$115.50
Purchase #5	$172.81	3.254%	$178.4332	$178.43	$178.45	$178.40
Purchase #6	$231.88	7.575%	$249.4449	$249.44	$249.45	$249.40
Purchase #7	$29.83	13.215%	$33.772	$33.77	$33.75	$33.80
7 purchase totals =	$652.89		$697.2481	$697.24	$697.25	$697.10