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	$138.45	6.814%	$147.884	$147.88	$147.90	$147.90
Purchase #2	$134.46	5.750%	$142.1915	$142.19	$142.20	$142.20
Purchase #3	$77.54	11.702%	$86.6137	$86.61	$86.60	$86.60
Purchase #4	$149.56	5.686%	$158.064	$158.06	$158.05	$158.10
Purchase #5	$227.33	9.761%	$249.5197	$249.52	$249.50	$249.50
Purchase #6	$5.97	8.371%	$6.4697	$6.47	$6.45	$6.50
Purchase #7	$207.85	5.107%	$218.4649	$218.46	$218.45	$218.50
7 purchase totals =	$941.16		$1,009.2075	$1,009.19	$1,009.15	$1,009.30