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	$43.82	3.721%	$45.4505	$45.45	$45.45	$45.50
Purchase #2	$82.52	12.826%	$93.104	$93.10	$93.10	$93.10
Purchase #3	$84.69	6.866%	$90.5048	$90.50	$90.50	$90.50
Purchase #4	$95.42	3.563%	$98.8198	$98.82	$98.80	$98.80
Purchase #5	$244.67	11.780%	$273.4921	$273.49	$273.50	$273.50
Purchase #6	$47.62	11.648%	$53.1668	$53.17	$53.15	$53.20
Purchase #7	$193.35	4.426%	$201.9077	$201.91	$201.90	$201.90
7 purchase totals =	$792.09		$856.4457	$856.44	$856.40	$856.50