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	$36.49	5.119%	$38.3579	$38.36	$38.35	$38.40
Purchase #2	$194.48	12.725%	$219.2276	$219.23	$219.25	$219.20
Purchase #3	$238.92	12.835%	$269.5854	$269.59	$269.60	$269.60
Purchase #4	$143.51	12.489%	$161.433	$161.43	$161.45	$161.40
Purchase #5	$61.46	4.862%	$64.4482	$64.45	$64.45	$64.40
Purchase #6	$179.71	6.618%	$191.6032	$191.60	$191.60	$191.60
Purchase #7	$31.82	5.413%	$33.5424	$33.54	$33.55	$33.50
7 purchase totals =	$886.39		$978.1977	$978.20	$978.25	$978.10