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	$59.62	12.191%	$66.8883	$66.89	$66.90	$66.90
Purchase #2	$232.91	9.554%	$255.1622	$255.16	$255.15	$255.20
Purchase #3	$113.42	13.655%	$128.9075	$128.91	$128.90	$128.90
Purchase #4	$234.60	9.665%	$257.2741	$257.27	$257.25	$257.30
Purchase #5	$228.43	6.650%	$243.6206	$243.62	$243.60	$243.60
Purchase #6	$181.71	6.279%	$193.1196	$193.12	$193.10	$193.10
Purchase #7	$170.86	6.453%	$181.8856	$181.89	$181.90	$181.90
7 purchase totals =	$1,221.55		$1,326.8579	$1,326.86	$1,326.80	$1,326.90