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	$35.94	5.285%	$37.8394	$37.84	$37.85	$37.80
Purchase #2	$39.41	12.803%	$44.4557	$44.46	$44.45	$44.50
Purchase #3	$102.83	12.526%	$115.7105	$115.71	$115.70	$115.70
Purchase #4	$231.29	10.310%	$255.136	$255.14	$255.15	$255.10
Purchase #5	$220.79	5.787%	$233.5671	$233.57	$233.55	$233.60
Purchase #6	$234.61	11.554%	$261.7168	$261.72	$261.70	$261.70
Purchase #7	$115.47	10.837%	$127.9835	$127.98	$128.00	$128.00
7 purchase totals =	$980.34		$1,076.4090	$1,076.42	$1,076.40	$1,076.40