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	$240.54	4.252%	$250.7678	$250.77	$250.75	$250.80
Purchase #2	$166.34	11.817%	$185.9964	$186.00	$186.00	$186.00
Purchase #3	$85.60	12.289%	$96.1194	$96.12	$96.10	$96.10
Purchase #4	$114.63	4.580%	$119.8801	$119.88	$119.90	$119.90
Purchase #5	$102.26	11.270%	$113.7847	$113.78	$113.80	$113.80
Purchase #6	$153.29	10.426%	$169.272	$169.27	$169.25	$169.30
Purchase #7	$138.25	11.110%	$153.6096	$153.61	$153.60	$153.60
7 purchase totals =	$1,000.91		$1,089.4300	$1,089.43	$1,089.40	$1,089.50