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	$14.64	12.548%	$16.477	$16.48	$16.50	$16.50
Purchase #2	$156.74	6.550%	$167.0065	$167.01	$167.00	$167.00
Purchase #3	$104.57	6.597%	$111.4685	$111.47	$111.45	$111.50
Purchase #4	$33.71	7.650%	$36.2888	$36.29	$36.30	$36.30
Purchase #5	$194.30	12.201%	$218.0065	$218.01	$218.00	$218.00
Purchase #6	$84.53	8.262%	$91.5139	$91.51	$91.50	$91.50
Purchase #7	$78.46	5.200%	$82.5399	$82.54	$82.55	$82.50
7 purchase totals =	$666.95		$723.3011	$723.31	$723.30	$723.30