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	$136.61	6.806%	$145.9077	$145.91	$145.90	$145.90
Purchase #2	$75.65	13.633%	$85.9634	$85.96	$85.95	$86.00
Purchase #3	$64.67	10.123%	$71.2165	$71.22	$71.20	$71.20
Purchase #4	$142.63	9.761%	$156.5521	$156.55	$156.55	$156.60
Purchase #5	$38.35	11.838%	$42.8899	$42.89	$42.90	$42.90
Purchase #6	$168.83	6.532%	$179.858	$179.86	$179.85	$179.90
Purchase #7	$115.27	4.502%	$120.4595	$120.46	$120.45	$120.50
7 purchase totals =	$742.01		$802.8471	$802.85	$802.80	$803.00