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	$147.90	12.376%	$166.2041	$166.20	$166.20	$166.20
Purchase #2	$228.32	13.712%	$259.6272	$259.63	$259.65	$259.60
Purchase #3	$110.29	11.564%	$123.0439	$123.04	$123.05	$123.00
Purchase #4	$116.86	5.480%	$123.2639	$123.26	$123.25	$123.30
Purchase #5	$38.44	13.204%	$43.5156	$43.52	$43.50	$43.50
Purchase #6	$154.44	13.152%	$174.7519	$174.75	$174.75	$174.80
Purchase #7	$175.28	6.185%	$186.1211	$186.12	$186.10	$186.10
7 purchase totals =	$971.53		$1,076.5277	$1,076.52	$1,076.50	$1,076.50