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	$79.35	7.639%	$85.4115	$85.41	$85.40	$85.40
Purchase #2	$203.55	13.220%	$230.4593	$230.46	$230.45	$230.50
Purchase #3	$24.60	3.733%	$25.5183	$25.52	$25.50	$25.50
Purchase #4	$178.48	5.434%	$188.1786	$188.18	$188.20	$188.20
Purchase #5	$156.45	5.403%	$164.903	$164.90	$164.90	$164.90
Purchase #6	$52.25	6.127%	$55.4514	$55.45	$55.45	$55.50
Purchase #7	$97.70	4.775%	$102.3652	$102.37	$102.35	$102.40
7 purchase totals =	$792.38		$852.2873	$852.29	$852.25	$852.40