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	$68.51	6.696%	$73.0974	$73.10	$73.10	$73.10
Purchase #2	$35.71	12.857%	$40.3012	$40.30	$40.30	$40.30
Purchase #3	$163.61	3.605%	$169.5081	$169.51	$169.50	$169.50
Purchase #4	$81.36	9.420%	$89.0241	$89.02	$89.00	$89.00
Purchase #5	$187.66	12.604%	$211.3127	$211.31	$211.30	$211.30
Purchase #6	$172.35	7.557%	$185.3745	$185.37	$185.35	$185.40
Purchase #7	$73.96	9.701%	$81.1349	$81.13	$81.15	$81.10
7 purchase totals =	$783.16		$849.7529	$849.74	$849.70	$849.70