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	$154.86	9.677%	$169.8458	$169.85	$169.85	$169.80
Purchase #2	$229.48	11.384%	$255.604	$255.60	$255.60	$255.60
Purchase #3	$211.90	7.402%	$227.5848	$227.58	$227.60	$227.60
Purchase #4	$131.46	8.642%	$142.8208	$142.82	$142.80	$142.80
Purchase #5	$28.42	12.420%	$31.9498	$31.95	$31.95	$31.90
Purchase #6	$64.29	10.672%	$71.151	$71.15	$71.15	$71.20
Purchase #7	$179.97	6.143%	$191.0256	$191.03	$191.05	$191.00
7 purchase totals =	$1,000.38		$1,089.9818	$1,089.98	$1,090.00	$1,089.90