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	$31.63	6.782%	$33.7751	$33.78	$33.80	$33.80
Purchase #2	$182.46	10.309%	$201.2698	$201.27	$201.25	$201.30
Purchase #3	$5.75	6.591%	$6.129	$6.13	$6.15	$6.10
Purchase #4	$167.93	8.699%	$182.5382	$182.54	$182.55	$182.50
Purchase #5	$78.90	13.521%	$89.5681	$89.57	$89.55	$89.60
Purchase #6	$114.91	7.595%	$123.6374	$123.64	$123.65	$123.60
Purchase #7	$186.76	10.632%	$206.6163	$206.62	$206.60	$206.60
7 purchase totals =	$768.34		$843.5339	$843.55	$843.55	$843.50