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	$87.73	13.575%	$99.6393	$99.64	$99.65	$99.60
Purchase #2	$85.90	7.689%	$92.5049	$92.50	$92.50	$92.50
Purchase #3	$181.29	9.253%	$198.0648	$198.06	$198.05	$198.10
Purchase #4	$169.90	12.135%	$190.5174	$190.52	$190.50	$190.50
Purchase #5	$127.92	10.453%	$141.2915	$141.29	$141.30	$141.30
Purchase #6	$232.46	12.550%	$261.6337	$261.63	$261.65	$261.60
Purchase #7	$230.52	8.789%	$250.7804	$250.78	$250.80	$250.80
7 purchase totals =	$1,115.72		$1,234.4320	$1,234.42	$1,234.45	$1,234.40