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	$179.92	6.643%	$191.8721	$191.87	$191.85	$191.90
Purchase #2	$63.57	12.215%	$71.3351	$71.34	$71.35	$71.30
Purchase #3	$17.29	7.148%	$18.5259	$18.53	$18.55	$18.50
Purchase #4	$212.59	11.392%	$236.8083	$236.81	$236.80	$236.80
Purchase #5	$72.87	12.503%	$81.9809	$81.98	$82.00	$82.00
Purchase #6	$236.71	9.251%	$258.608	$258.61	$258.60	$258.60
Purchase #7	$17.57	4.771%	$18.4083	$18.41	$18.40	$18.40
7 purchase totals =	$800.52		$877.5386	$877.55	$877.55	$877.50