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	$129.67	3.261%	$133.8985	$133.90	$133.90	$133.90
Purchase #2	$50.80	5.106%	$53.3938	$53.39	$53.40	$53.40
Purchase #3	$18.98	9.526%	$20.788	$20.79	$20.80	$20.80
Purchase #4	$43.54	3.357%	$45.0016	$45.00	$45.00	$45.00
Purchase #5	$95.56	3.126%	$98.5472	$98.55	$98.55	$98.50
Purchase #6	$51.27	7.504%	$55.1173	$55.12	$55.10	$55.10
Purchase #7	$106.37	6.847%	$113.6532	$113.65	$113.65	$113.70
7 purchase totals =	$496.19		$520.3996	$520.40	$520.40	$520.40