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	$25.83	4.223%	$26.9208	$26.92	$26.90	$26.90
Purchase #2	$211.44	12.724%	$238.3436	$238.34	$238.35	$238.30
Purchase #3	$171.82	6.420%	$182.8508	$182.85	$182.85	$182.90
Purchase #4	$77.37	5.134%	$81.3422	$81.34	$81.35	$81.30
Purchase #5	$70.40	11.644%	$78.5974	$78.60	$78.60	$78.60
Purchase #6	$239.75	12.842%	$270.5387	$270.54	$270.55	$270.50
Purchase #7	$219.82	13.530%	$249.5616	$249.56	$249.55	$249.60
7 purchase totals =	$1,016.43		$1,128.1551	$1,128.15	$1,128.15	$1,128.10