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	$78.75	10.577%	$87.0794	$87.08	$87.10	$87.10
Purchase #2	$161.65	7.235%	$173.3454	$173.35	$173.35	$173.30
Purchase #3	$71.69	9.293%	$78.3522	$78.35	$78.35	$78.40
Purchase #4	$72.96	7.597%	$78.5028	$78.50	$78.50	$78.50
Purchase #5	$218.99	10.648%	$242.3081	$242.31	$242.30	$242.30
Purchase #6	$105.92	13.729%	$120.4618	$120.46	$120.45	$120.50
Purchase #7	$36.83	9.442%	$40.3075	$40.31	$40.30	$40.30
7 purchase totals =	$746.79		$820.3572	$820.36	$820.35	$820.40