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	$168.90	10.844%	$187.2155	$187.22	$187.20	$187.20
Purchase #2	$156.65	11.860%	$175.2287	$175.23	$175.25	$175.20
Purchase #3	$109.62	4.243%	$114.2712	$114.27	$114.25	$114.30
Purchase #4	$20.60	4.639%	$21.5556	$21.56	$21.55	$21.60
Purchase #5	$60.30	3.347%	$62.3182	$62.32	$62.30	$62.30
Purchase #6	$197.51	6.621%	$210.5871	$210.59	$210.60	$210.60
Purchase #7	$126.73	8.112%	$137.0103	$137.01	$137.00	$137.00
7 purchase totals =	$840.31		$908.1866	$908.20	$908.15	$908.20