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	$148.60	13.398%	$168.5094	$168.51	$168.50	$168.50
Purchase #2	$63.28	13.649%	$71.9171	$71.92	$71.90	$71.90
Purchase #3	$171.63	8.514%	$186.2426	$186.24	$186.25	$186.20
Purchase #4	$183.91	3.677%	$190.6724	$190.67	$190.65	$190.70
Purchase #5	$57.32	12.740%	$64.6226	$64.62	$64.60	$64.60
Purchase #6	$236.36	13.857%	$269.1124	$269.11	$269.10	$269.10
Purchase #7	$62.48	9.179%	$68.215	$68.22	$68.20	$68.20
7 purchase totals =	$923.58		$1,019.2915	$1,019.29	$1,019.20	$1,019.20