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	$67.86	8.777%	$73.8161	$73.82	$73.80	$73.80
Purchase #2	$233.71	5.798%	$247.2605	$247.26	$247.25	$247.30
Purchase #3	$122.70	11.721%	$137.0817	$137.08	$137.10	$137.10
Purchase #4	$89.98	13.740%	$102.3433	$102.34	$102.35	$102.30
Purchase #5	$78.83	12.320%	$88.5419	$88.54	$88.55	$88.50
Purchase #6	$179.64	3.332%	$185.6256	$185.63	$185.65	$185.60
Purchase #7	$92.96	7.508%	$99.9394	$99.94	$99.95	$99.90
7 purchase totals =	$865.68		$934.6085	$934.61	$934.65	$934.50