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	$36.94	12.604%	$41.5959	$41.60	$41.60	$41.60
Purchase #2	$232.73	7.615%	$250.4524	$250.45	$250.45	$250.50
Purchase #3	$109.85	4.737%	$115.0536	$115.05	$115.05	$115.10
Purchase #4	$78.46	5.616%	$82.8663	$82.87	$82.85	$82.90
Purchase #5	$139.37	12.558%	$156.8721	$156.87	$156.85	$156.90
Purchase #6	$68.84	4.755%	$72.1133	$72.11	$72.10	$72.10
Purchase #7	$87.63	5.477%	$92.4295	$92.43	$92.45	$92.40
7 purchase totals =	$753.82		$811.3831	$811.38	$811.35	$811.50