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	$127.60	12.237%	$143.2144	$143.21	$143.20	$143.20
Purchase #2	$239.31	10.384%	$264.16	$264.16	$264.15	$264.20
Purchase #3	$39.62	9.360%	$43.3284	$43.33	$43.35	$43.30
Purchase #4	$98.71	4.256%	$102.9111	$102.91	$102.90	$102.90
Purchase #5	$198.89	4.532%	$207.9037	$207.90	$207.90	$207.90
Purchase #6	$89.52	7.686%	$96.4005	$96.40	$96.40	$96.40
Purchase #7	$136.61	3.822%	$141.8312	$141.83	$141.85	$141.80
7 purchase totals =	$930.26		$999.7493	$999.74	$999.75	$999.70