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	$74.36	11.424%	$82.8549	$82.85	$82.85	$82.90
Purchase #2	$227.55	7.860%	$245.4354	$245.44	$245.45	$245.40
Purchase #3	$62.53	7.159%	$67.0065	$67.01	$67.00	$67.00
Purchase #4	$119.86	12.482%	$134.8209	$134.82	$134.80	$134.80
Purchase #5	$19.88	4.710%	$20.8163	$20.82	$20.80	$20.80
Purchase #6	$213.26	8.326%	$231.016	$231.02	$231.00	$231.00
Purchase #7	$118.39	12.458%	$133.139	$133.14	$133.15	$133.10
7 purchase totals =	$835.83		$915.0890	$915.10	$915.05	$915.00