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	$28.59	9.770%	$31.3832	$31.38	$31.40	$31.40
Purchase #2	$184.81	11.827%	$206.6675	$206.67	$206.65	$206.70
Purchase #3	$195.28	7.807%	$210.5255	$210.53	$210.55	$210.50
Purchase #4	$214.56	3.718%	$222.5373	$222.54	$222.55	$222.50
Purchase #5	$171.57	7.527%	$184.4841	$184.48	$184.50	$184.50
Purchase #6	$222.79	10.260%	$245.6483	$245.65	$245.65	$245.60
Purchase #7	$132.79	3.147%	$136.9689	$136.97	$136.95	$137.00
7 purchase totals =	$1,150.39		$1,238.2148	$1,238.22	$1,238.25	$1,238.20