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	$78.61	9.361%	$85.9687	$85.97	$85.95	$86.00
Purchase #2	$35.33	8.192%	$38.2242	$38.22	$38.20	$38.20
Purchase #3	$170.89	12.772%	$192.7161	$192.72	$192.70	$192.70
Purchase #4	$59.97	9.150%	$65.4573	$65.46	$65.45	$65.50
Purchase #5	$101.88	11.311%	$113.4036	$113.40	$113.40	$113.40
Purchase #6	$71.90	12.725%	$81.0493	$81.05	$81.05	$81.00
Purchase #7	$83.98	7.576%	$90.3423	$90.34	$90.35	$90.30
7 purchase totals =	$602.56		$667.1615	$667.16	$667.10	$667.10